What’s the difference in the Seiko 5 models and the Prospex divers?
The 5 is a Seiko’s budget mechanical range, almost all have 7s26/7s36 movements so not hacking or hand windable, but more importantly where they’re dive watch “inspired” they’re typically only WR to 100m at best. There are dozens of 5s and they come in all sorts not just dive styles, there’s dress, field, pilot, you name it.
Prospex is sort of Seiko’s mid-range, with a significant quality step up. Better finishing, better movements, better WR (often actually dive certified), and often with sapphire instead of Hardlex. Again though, Prospex covers all styles, not just dive.