Frederique Constant Slimline Moonphase Manufacture vs Casio G-Shock GA-B2100 CasiOak
Frederique Constant's dress watch meets Casio's diver
Quick Verdict
The Casio G-Shock GA-B2100 CasiOak ($100–$150) delivers Casio Quartz (Solar-Powered) technology in the tier below the Frederique Constant Slimline Moonphase Manufacture ($2,500–$5,000). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Slimline Moonphase Manufacture justifies its premium with Swiss Made heritage and Automatic FC-705 (In-House). Both represent excellent choices in the luxury watch category.
Transparency — We earn a small commission on purchases made through our Amazon links. This doesn't affect our editorial independence.
Specifications Compared
| Feature | Frederique Constant Slimline Moonphase Manufacture | Casio G-Shock GA-B2100 CasiOak |
|---|---|---|
| Price | $2,500–$5,000 | $100–$150 |
| Case Size | 42mm | 45.4mm (48.5mm lug-to-lug, 11.9mm thick) |
| Movement | Automatic FC-705 (In-House) | Quartz Module 5689 (Tough Solar + Bluetooth) |
| Caliber Type | In-House Automatic Manufacture | Casio Quartz (Solar-Powered) |
| Power Reserve | 42 Hours | About 7 months on a full charge without light; about 18 months in power-saving (Casio) |
| Water Resistance | 30m (3 ATM) | 200m (20 ATM) |
| Crystal | Convex Sapphire | Mineral Glass |
| Case Material | Stainless Steel | Carbon Core Guard Resin |
| Origin | Swiss Made | Made in Japan |
Category-by-Category Analysis
Design & Aesthetics
Frederique Constant's design language vs Casio's approach
The Frederique Constant Slimline Moonphase Manufacture features a Stainless Steel case at 42mm with Convex Sapphire protection. The Casio G-Shock GA-B2100 CasiOak offers Carbon Core Guard Resin construction at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with Mineral Glass. Both represent their brand's distinct design philosophy and heritage.
Movement & Performance
Automatic FC-705 (In-House) vs Quartz Module 5689 (Tough Solar + Bluetooth)
The Slimline Moonphase Manufacture runs the Automatic FC-705 (In-House) (In-House Automatic Manufacture, 42 Hours power reserve) at 28,800 vph (4 Hz) frequency. The G-Shock GA-B2100 CasiOak uses the Quartz Module 5689 (Tough Solar + Bluetooth) (Casio Quartz (Solar-Powered), About 7 months on a full charge without light; about 18 months in power-saving (Casio) reserve) at standard. The Slimline Moonphase Manufacture edges ahead on power reserve.
Wearability & Fit
42mm vs 45.4mm (48.5mm lug-to-lug, 11.9mm thick) — different wrist presence
At 42mm, the Slimline Moonphase Manufacture wears more compactly on smaller wrists compared to the G-Shock GA-B2100 CasiOak at 45.4mm (48.5mm lug-to-lug, 11.9mm thick). Water resistance differs: 30m (3 ATM) vs 200m (20 ATM).
Value & Cost of Ownership
Casio sits in the lower tier
The Frederique Constant Slimline Moonphase Manufacture sits at $2,500–$5,000 and the Casio G-Shock GA-B2100 CasiOak at $100–$150. On the specs that outlast any price: the Slimline Moonphase Manufacture uses Convex Sapphire with 42 Hours, against Mineral Glass and About 7 months on a full charge without light; about 18 months in power-saving (Casio) on the G-Shock GA-B2100 CasiOak. Service intervals are typically 5-7 years for both.
Water Resistance
30m (3 ATM) vs 200m (20 ATM)
The Slimline Moonphase Manufacture is rated to 30m (3 ATM) while the G-Shock GA-B2100 CasiOak handles 200m (20 ATM). The G-Shock GA-B2100 CasiOak offers superior water resistance.
Materials Face-Off
| Component | Frederique Constant Slimline Moonphase Manufacture | Casio G-Shock GA-B2100 CasiOak |
|---|---|---|
| Case alloy | Stainless steel 316L (standard mid-range Swiss spec) | Casio's proprietary monocoque case technology integrating carbon fibers into fine resin. The carbon fibers dramatically raise the tensile strength and modulus of elasticity of the case structure, allowing the GA-2100 to achieve an 11.8mm thickness — the thinnest analog G-Shock at launch — while maintaining full 10m drop impact resistance. Total case weight: 51g. |
| Crystal | Synthetic sapphire grown via Verneuil process, Mohs 9, convex (domed) profile, anti-reflective coating Mohs 9 | Flat mineral glass with Mohs hardness ~6. Thermally tempered for impact resistance — flexes under force rather than shattering like sapphire. Not scratch-proof, but replacement crystals cost ~$10. |
| Lume specification | None (dress watch by design) | Durable urethane polymer resistant to sweat, saltwater, UV radiation, and skin oils. Features quick-release spring bars. Known to last 5–10 years with daily wear before degradation. |
| Dial finishing | Silver lacquer with applied indices and printed moonphase graphic + pointer date scale | Secured by 4 Phillips screws for 200m (20 ATM) water resistance. The GA-B2100 is Tough Solar: a rechargeable cell topped up by any light, so there is no coin cell to swap. Casio rates a full charge at about seven months of normal use without light, and about eighteen months in power-saving. |
| Strap | Black or brown calfskin leather with signed Frederique Constant buckle | The luxury MRG-B2100 variant ($3,500+), hand-assembled at Yamagata Casio's Premium Production Line (PPL) by certified "Medalist" craftsmen, uses Cobarion® (cobalt-chromium alloy, 4× harder than pure titanium) bezels and DAT55G titanium (3× harder than pure titanium) bracelet links. |
Cost of Ownership Compared
Who Should Pick Which
Pick the Frederique Constant Slimline Moonphase Manufacture if…
- Those who prioritize scratch resistance — sapphire crystal
- Dress watch seekers who want understated elegance
Pick the Casio G-Shock GA-B2100 CasiOak if…
- Anyone wanting an indestructible daily beater under $100 with serious design credibility
- Water sports enthusiasts — 200m WR with G-Shock shockproofing
- Watch modding enthusiasts — massive aftermarket ecosystem of metal conversion kits
- High-end collectors needing a dedicated beater alongside their luxury pieces
Frederique Constant Slimline Moonphase Manufacture
- Brand recognition below heritage Swiss brands — Longines (1832), Omega, Tudor have stronger name recognition. FC (1988 founding) is a younger brand without the same cultural footprint despite genuine in-house horological credentials
- 42mm wears large for traditional dress watch — modern preference is often 38–40mm for dress; 42mm + slim bezel pushes visual presence larger
- 21mm lug width awkward for aftermarket strap fitment
- 30m WR limits to pure dress use — no swimming, no shower
Casio G-Shock GA-B2100 CasiOak
- Stealth-black legibility deficit: The GA2100-1A1 has absolutely no Neobrite luminescent paint on hands or indices. Low-light readability is poor — you must rely entirely on the Double LED Super Illuminator.
- Mineral glass scratches: Not sapphire. Daily beater use will accumulate minor scuffs over time. Replacement crystals are cheap (~$10) but require caseback removal.
- Tiny digital subdisplay: The LCD window at 4:30 is small and genuinely difficult to read for anyone with less than perfect vision. The Hand-Shift feature (sweeps hands to 7:35 position to clear the LCD) helps but isn't a substitute for a full digital display.
- Module 5689 is quartz: For mechanical-watch purists, this is a non-starter. For everyone else, it's a feature — better accuracy (±15 sec/month), no winding, no expensive servicing, and solar charging that never needs a battery change.
Our Verdict
Frederique Constant
Slimline Moonphase Manufacture
Choose the Frederique Constant Slimline Moonphase Manufacture if you prioritize In-House Automatic Manufacture engineering, Swiss Made craftsmanship, and 30m (3 ATM) water resistance. At $2,500–$5,000, it delivers Automatic FC-705 (In-House) with 42 Hours power reserve.
Check Price on AmazonCasio
G-Shock GA-B2100 CasiOak
Choose the Casio G-Shock GA-B2100 CasiOak if you value Casio Quartz (Solar-Powered) technology, Made in Japan heritage, and 45.4mm (48.5mm lug-to-lug, 11.9mm thick) proportions. At $100–$150, the Quartz Module 5689 (Tough Solar + Bluetooth) with About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve makes it a compelling choice.
Check Price on AmazonThe Bottom Line
The Frederique Constant Slimline Moonphase Manufacture and Casio G-Shock GA-B2100 CasiOak represent two distinct approaches to fine watchmaking — the Frederique Constant bringing Swiss Made tradition while Casio delivers Made in Japan engineering.
Frequently Asked Questions
More Comparisons
Explore These Watches
How This Page Was Made
Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.