Lots of different models, it's hard to generalise.
Best ones to go for in my opinion are the cal 601/613 handwounds from the 60s. The automatics are more desirable but can be a lot more costly to sort out. I`d also recommend something waterproof; some of the watches were supposedly dustproof, they won`t stand up to being submerged but they may withstand splashed water if you're lucky.
Look for a dial in good original condition with a good handset; replacement hands are a bit hit and miss, genuine ones are getting harder to source and the generics aren`t always exactly the same. Reluming hands isn`t a problem, or repainting if they're black-filled, but pitted/badly tarnished hands have to be replaced to look right again. Refinishing a scruffy dial costs around £100 and the result isn`t always exactly the same. Avoid heavily dinged/battered cases, even after refinishing they won`t be perfect again if the damage is deep.
Good ones are getting harder to find thesedays at reasonable money.
Paul