Citizen Promaster Sea Eco-Drive Diver vs Casio G-Shock GA-B2100 CasiOak
Two divers compared — $250–$500 vs $100–$150
Quick Verdict
The Casio G-Shock GA-B2100 CasiOak ($100–$150) delivers Casio Quartz (Solar-Powered) technology in the tier below the Citizen Promaster Sea Eco-Drive Diver ($250–$500). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Promaster Sea Eco-Drive Diver justifies its premium with Made in Japan heritage and Eco-Drive Caliber E168. Both represent excellent choices in the diver category.
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Specifications Compared
| Feature | Citizen Promaster Sea Eco-Drive Diver | Casio G-Shock GA-B2100 CasiOak |
|---|---|---|
| Price | $250–$500 | $100–$150 |
| Case Size | 44mm | 45.4mm (48.5mm lug-to-lug, 11.9mm thick) |
| Movement | Eco-Drive Caliber E168 | Quartz Module 5689 (Tough Solar + Bluetooth) |
| Caliber Type | Citizen Eco-Drive (Solar Quartz) | Casio Quartz (Solar-Powered) |
| Power Reserve | — | About 7 months on a full charge without light; about 18 months in power-saving (Casio) |
| Water Resistance | 200m (20 ATM) ISO 6425 | 200m (20 ATM) |
| Crystal | Mineral Crystal | Mineral Glass |
| Case Material | Stainless Steel | Carbon Core Guard Resin |
| Origin | Made in Japan | Made in Japan |
Category-by-Category Analysis
Design & Aesthetics
Citizen's design language vs Casio's approach
The Citizen Promaster Sea Eco-Drive Diver features a Stainless Steel case at 44mm with Mineral Crystal 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
Eco-Drive Caliber E168 vs Quartz Module 5689 (Tough Solar + Bluetooth)
The Promaster Sea Eco-Drive Diver runs the Eco-Drive Caliber E168 (Citizen Eco-Drive (Solar Quartz), standard power reserve) at standard 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 G-Shock GA-B2100 CasiOak offers a longer power reserve.
Wearability & Fit
44mm vs 45.4mm (48.5mm lug-to-lug, 11.9mm thick) — different wrist presence
At 44mm, the Promaster Sea Eco-Drive Diver 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: 200m (20 ATM) ISO 6425 vs 200m (20 ATM).
Value & Cost of Ownership
Casio sits in the lower tier
The Citizen Promaster Sea Eco-Drive Diver sits at $250–$500 and the Casio G-Shock GA-B2100 CasiOak at $100–$150. On the specs that outlast any price: the Promaster Sea Eco-Drive Diver uses Mineral Crystal with a standard reserve, 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
200m (20 ATM) ISO 6425 vs 200m (20 ATM)
The Promaster Sea Eco-Drive Diver is rated to 200m (20 ATM) ISO 6425 while the G-Shock GA-B2100 CasiOak handles 200m (20 ATM). Both offer identical water resistance ratings.
Our Verdict
Citizen
Promaster Sea Eco-Drive Diver
Choose the Citizen Promaster Sea Eco-Drive Diver if you prioritize Citizen Eco-Drive (Solar Quartz) engineering, Made in Japan craftsmanship, and 200m (20 ATM) ISO 6425 water resistance. At $250–$500, it delivers Eco-Drive Caliber E168 with solid 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 Citizen Promaster Sea Eco-Drive Diver and Casio G-Shock GA-B2100 CasiOak represent two distinct approaches to the diver category — the Citizen bringing Made in Japan tradition while Casio 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.