Tied at 88, and still not a coin flip.

Run the HypeScore math on these two and the totals land in the same place: 88 apiece. Nothing else about them lands in the same place. One is a $100-150 solar quartz square that will outlive its owner. The other is a $300-395 automatic that clears a dive certification almost nothing under $500 bothers with.

The GW-M5610U is the square G-Shock updated for a world with atomic clocks in it: Tough Solar charging so it never needs a battery, Multi-Band 6 radio sync so it never needs setting, 200 meters of resistance wrapped in a case that has survived four decades of abuse. The NY0086 runs a different argument entirely. Its Miyota 8203 hacks and hand winds at 21,600vph under a 200 meter rating that is ISO-compliant Diver’s, a testing regime rather than a pressure claim, which is the reason its Atlas entry calls it the value benchmark of the dive class.

Every line below is a published specification rather than an impression, and the bronze rule marks the side the specification favours. Where neither side wins, the row says so and stays quiet about it.

Which is the better buy, the Casio G-Shock GW-M5610U or the Citizen Promaster NY0086?

For most people, the Casio. It costs well under half what the Citizen does, it needs no service interval, no battery and no regulation, and 200 meters is 200 meters for anyone who is not specifically chasing a dive certification. Buy the Citizen instead if that certification, or a mechanical movement full stop, is the actual reason you clicked.

Is the Citizen’s ISO-compliant 200m rating actually better than the Casio’s 200m?

For diving, yes. ISO 6425 tests condensation resistance, shock, magnetic resistance and legibility in the dark, not just depth. The GW-M5610U’s 200m is a genuine engineering spec, Casio does not print numbers it cannot back, but it is a pressure rating rather than a certified testing regime. Neither watch is a substitute for a dedicated dive computer, but only one of them has papers.

Can the GW-M5610U’s resin band take a standard aftermarket strap?

No. The case and band are integrated, so there is no lug width to shop against and no strap market to raid. That is the trade the low price and the indestructibility both come from, and it is the row the Citizen wins outright: a 20mm lug and standard spring bars mean the NY0086 can wear a different strap every day of the week.

Does the Citizen Promaster NY0086 need to be wound or serviced like other automatics?

It winds itself on the wrist and hand winds if it stops, and Citizen does not publish a power reserve figure for it in any source we could verify, so treat a few days off the wrist as the point where it needs a shake. Like most automatics in this price class it will eventually want a service, a cost and a wait the Casio never asks for.

Is a Tough Solar quartz watch a legitimate alternative to a mechanical dive watch?

For most owners, yes, and the movement row above marks it a tie rather than a loss precisely because the two solve different problems well. The Casio wins on accuracy and zero maintenance, the Citizen wins on mechanical feel and mod culture. Buy the G-Shock if the watch on your wrist is a tool; buy the Promaster if it is also a hobby.