There are many real reasons to not use a small airline with a small fleet. Recovery from even a single canceled flight can be a nightmare for those holding tickets with a schedule to keep.

In this case aircraft maintenance will be overseen by the US regulators, the British regulators, the insurance underwriters, and likely a bank holding a loan on the hulls.

I would not buy any tickets on this airline that I could not afford to throw away and buy my ticket in or out on a major airline.

Before you pay for any airline tickets you should always check to see what interline agreements the airline has in place and who will take you ticket to get you home in the event your airline cannot fly.