I flew IC from EIS to SJU in February and while this doesn't speak to your original question, one big difference was re: carry on.

The major airlines usually say you can carry on one bag and one personal item. With IC you could only carry on one item. I travel with a small pack and a guitar which is fine for the major airlines (Air Canada, United, American) but IC made me check one so I was scrambling at the counter to move meds, car keys into guitar case (I wasn't going to check soft shelled cases guitar).

The flight was half full and the guitar wouldn't fit in overhead so the attendant said put it in empty seat beside me which I don't think would fly (pun intended) back home as it is safety hazard if plane crashes.

FYI Seaborne let me take 2 items to plane but one was sky checked so I picked it up at EIS ramp.

Don