To Translate Lostboy…
Yes, most of us are employees of one company, there are others who are self employed or others who work through an Agency but the majority of ROV people work for one company.
No, most of us get allocated a system (or sometimes one type of system) and work with that system (or systems) the majority of the time.
And no, you normally have a contract that says they expoect you to work x number of days. No company will guarantee x weeks on x weeks off, most with "try" and run an equal time on/off rota but it doesnt always work that way and they wont guarantee it. On a fixed platform you get helicopters regularly so crewchange dates are easier to plane but if you work on a boat, if the boat is not alongside when you are due off – you dont get off.