We went to Tobago a couple of years ago with BWEE to POS and then onward with Tobago Express. The A340 was a bit tatty on the inside and not much of the inflight entertainment worked but it was cheap and we got there and back.
Its a great prospect to be able to go from BFS direct but if you are planning to go to Tobago it looks like you`re gonna be stuck on Trinidad for the first night as there are no flights out of POS after 21.15 ish.