My info may be out of date, since it was a few years ago I was Caribbean-based.
They have a good reputation, good safety record as far as I am aware.
A few years ago they mainly operated DHC-6's. Dunno about the type-raing, but in that part of the world it wouldn't do any harm. I would expect pay to be standard Caribbean awful, but the experience and airmanship gained is always good.
Sint Maarten is not a bad place to be based at all. They had other bases as well - St. Kitts and Anguilla, I think. Those are more primitive, but if you can handle that, it would be my preference since cost of living is MUCH lower than SXM and you can always go over there free on shopping trips.
The Twotter is one of those aircraft that is always a good rating to have in that part of the world, and, I suspect, probably fairly cheap to obtain. For aircraft usage in the UK and a TRE, I'd contact British Antarctic Survey.