Casio G-Shock GA-B2100 CasiOak vs Seiko Prospex Samurai SRPL13
Two divers compared — $100–$150 vs $500–$1,000
Quick Verdict
The Casio G-Shock GA-B2100 CasiOak ($100–$150) offers Casio Quartz (Solar-Powered) precision in the tier below the Seiko Prospex Samurai SRPL13 ($500–$1,000). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Prospex Samurai SRPL13 counters with Made in Japan craftsmanship and 200m (20 ATM) water resistance. Both are exceptional divers for their respective tiers.
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Specifications Compared
| Feature | Casio G-Shock GA-B2100 CasiOak | Seiko Prospex Samurai SRPL13 |
|---|---|---|
| Price | $100–$150 | $500–$1,000 |
| Case Size | 45.4mm (48.5mm lug-to-lug, 11.9mm thick) | 41.7mm |
| Movement | Quartz Module 5689 (Tough Solar + Bluetooth) | Automatic Caliber 4R35 |
| Caliber Type | Casio Quartz (Solar-Powered) | Seiko In-House Automatic |
| Power Reserve | About 7 months on a full charge without light; about 18 months in power-saving (Casio) | 41 Hours |
| Water Resistance | 200m (20 ATM) | 200m (20 ATM) |
| Crystal | Mineral Glass | Hardlex Crystal |
| Case Material | Carbon Core Guard Resin | Stainless Steel |
| Origin | Made in Japan | Made in Japan |
Category-by-Category Analysis
Design & Aesthetics
Casio's design language vs Seiko's approach
The Casio G-Shock GA-B2100 CasiOak features a Carbon Core Guard Resin case at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with Mineral Glass protection. The Seiko Prospex Samurai SRPL13 offers Stainless Steel construction at 41.7mm with Hardlex Crystal. Both represent their brand's distinct design philosophy and heritage.
Movement & Performance
Quartz Module 5689 (Tough Solar + Bluetooth) vs Automatic Caliber 4R35
The G-Shock GA-B2100 CasiOak runs 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) power reserve) at standard frequency. The Prospex Samurai SRPL13 uses the Automatic Caliber 4R35 (Seiko In-House Automatic, 41 Hours reserve) at 21,600 vph (3 Hz). The Prospex Samurai SRPL13 offers a longer power reserve.
Wearability & Fit
45.4mm (48.5mm lug-to-lug, 11.9mm thick) vs 41.7mm — different wrist presence
At 45.4mm (48.5mm lug-to-lug, 11.9mm thick), the G-Shock GA-B2100 CasiOak has a bolder wrist presence compared to the Prospex Samurai SRPL13 at 41.7mm. Water resistance differs: 200m (20 ATM) vs 200m (20 ATM).
Value & Cost of Ownership
Casio sits in the lower tier
The Casio G-Shock GA-B2100 CasiOak sits at $100–$150 and the Seiko Prospex Samurai SRPL13 at $500–$1,000. On the specs that outlast any price: the G-Shock GA-B2100 CasiOak uses Mineral Glass with About 7 months on a full charge without light; about 18 months in power-saving (Casio), against Hardlex Crystal and 41 Hours on the Prospex Samurai SRPL13. Service intervals are typically 5-7 years for both.
Water Resistance
200m (20 ATM) vs 200m (20 ATM)
The G-Shock GA-B2100 CasiOak is rated to 200m (20 ATM) while the Prospex Samurai SRPL13 handles 200m (20 ATM). Both offer identical water resistance ratings.
Our Verdict
Casio
G-Shock GA-B2100 CasiOak
Choose the Casio G-Shock GA-B2100 CasiOak if you prioritize Casio Quartz (Solar-Powered) engineering, Made in Japan craftsmanship, and 200m (20 ATM) water resistance. At $100–$150, it delivers 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.
Check Price on AmazonSeiko
Prospex Samurai SRPL13
Choose the Seiko Prospex Samurai SRPL13 if you value Seiko In-House Automatic technology, Made in Japan heritage, and 41.7mm proportions. At $500–$1,000, the Automatic Caliber 4R35 with 41 Hours power reserve makes it a compelling choice.
Check Price on AmazonThe Bottom Line
The Casio G-Shock GA-B2100 CasiOak and Seiko Prospex Samurai SRPL13 represent two distinct approaches to the diver category — the Casio bringing Made in Japan tradition while Seiko delivers Made in Japan engineering.
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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.