Formex Reef 39.5 mmvsSeiko Prospex Marinemaster 1965 Heritage Diver's Watch
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Measurements
Catalog photos are all shot at the same flattering size. These aren't: every case below shares one millimeter scale.

Reef 39.5 mm

Prospex Marinemaster 1965 Heritage Diver's Watch
Diameter
39.5mm
39.5mm
Lug-to-Lug
45.5mm
lowest
47.2mm
Thickness
11mm
lowest
12.3mm
Water Resistance
300m
highest
200m
Power Reserve
56h
highest
45h
MSRP
$2,230
lowest
$2,800
Movement
Sellita SW300-1
Seiko 6L37
Case
4 specsCrystal & Dial
4 specsMovement
3 specsPricing
1 specsReviews
Synthesized for each watch independently from owner discussions, enthusiast forums, written reviews, and video reviewers.
The Formex Reef 39.5 mm is widely praised for its refined finishing, improved proportions, and compelling value under €2,000. Owners and reviewers highlight its comfortable wearability on smaller wrists, unique aesthetic, and impressive specifications including 300m water resistance and a COSC-certified Sellita SW300-1 movement. Some note the 22mm lug width feels slightly disproportionate and the bracelet could benefit from more taper. A prototype crown protrusion issue is expected to be resolved in production. Overall, owners rate the Formex Reef 39.5 mm highly for its excellent build quality and tool-like features at its price point.
The Seiko Prospex Marinemaster Marinemaster 1965 Heritage Diver's Watch is praised for its modern execution of a classic design, with reviewers noting the appealing 39.5mm case size and updated bracelet that improve wearability. Some reviewers mention the 6L37 movement has a 46-hour power reserve, with accuracy rated around -10/+15 seconds per day. A drawback identified by reviewers is the lack of tool-free micro-adjustment on the clasp. Overall, owners and reviewers find the Seiko Prospex Marinemaster Marinemaster 1965 Heritage Diver's Watch to be a handsome re-interpretation of a beloved design, with its improved wearability being a key strength.
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