I think the key question is, how much power do want from your car which determines what FMIC would suit best?
if its up to 300bhp and you are on a budget (which I see you are), then the ebay ones will be fine
if you are going BT, then the tried and tested route of the Forge or PA kit is better. PA kit IMO is better suited for BT applications
I think I read somewhere from someone on here that the ebay kits were too small for BT applications....as expected I suppose, as they are not that big