Which is cheaper, the Formex Reef 39.5 mm or the Seiko 5KX?

At MSRP the Seiko 5KX is the cheaper of the two at $350, against $2,230 for the Formex Reef 39.5 mm — a $1,880 gap before any retailer discounting.

Which is bigger, the Formex Reef 39.5 mm or the Seiko 5KX?

The Seiko 5KX wears larger at 42.5mm versus 39.5mm for the Formex Reef 39.5 mm — a 3mm difference across the dial.

Which has better water resistance, the Formex Reef 39.5 mm or the Seiko 5KX?

The Formex Reef 39.5 mm is rated to 300m versus 10m for the Seiko 5KX.

Which has a longer power reserve, the Formex Reef 39.5 mm or the Seiko 5KX?

The Formex Reef 39.5 mm carries a 56-hour power reserve against 41 hours on the Seiko 5KX.

What movement does the Formex Reef 39.5 mm run compared to the Seiko 5KX?

Both watches run automatic movements — the Formex Reef 39.5 mm uses the Sellita SW300-1 and the Seiko 5KX uses the Seiko 4R36.

Side by side

Formex Reef 39.5 mmvsSeiko 5KX

The numbers, the dial colors, the calibers — laid out so you can stop flipping between tabs.

Add a watch

Formex Reef 39.5 mm

MSRP $2,230

See the full Reef 39.5 mm

MSRP $350

What people say

Owners + reviewers, side by side

Synthesized for each watch independently from owner discussions, enthusiast forums, written reviews, and video reviewers.

Formex Reef 39.5 mm

The Formex Reef 39.5 mm is widely praised for its refined finishing, comfortable and well-proportioned case design, and impressive specifications for its price point, including COSC-certified Sellita SW300-1 movement and 300m water resistance. Owners and reviewers highlight the tool-less micro-adjust clasp and quick-release spring bars as practical features. Some reviewers note that the 22mm lug width feels slightly disproportionate to the smaller case, and the bracelet could benefit from more taper, though this is a point of contention for some owners who value the overall package. A prototype crown protrusion issue is noted as being addressed for production. On balance, owners and reviewers rate the Formex Reef 39.5 mm highly for its excellent value and well-executed design.

Owners widely praise the Seiko 5 Sports SKX series for its strong lume and comfortable wearability, with many noting its compact feel due to a short lug-to-lug length. The NH36 movement's accuracy varies, with typical performance between +/-5 to 10 seconds per day, though some report better. A lack of screw-down crown and ISO certification are noted drawbacks for its water resistance. Some owners find the bracelet to be of cheaper construction with hollow links, and a few have reported quality control issues. The consensus is that the Seiko 5 Sports SKX series offers good value for its price, appealing to those who appreciate its tool-like nature and iconic lineage.