No doubt the wise like Bezelbub will sniff out a better deal after much searching, but for everyone else 10 minutes on the atpl finance website will give an answer as to if finance is available at very short notice.
I think RTN11 addresses the point quite succinctly. This loan does appear to lock you in to the one provider (unless they go bust or you lose your medical.) That raises the first red flag. It is also "offered" at a rate nearly twice that of the best unsecured loans on the market. However that needs to be balanced against the creditworthiness of the applicant. Even so, it is only a "representative" rate, so presumably the loan rate (if offered at all) also depends on the applicants credit score?
The loan does restore some of the "section 75" protections that a credit card purchase might ordinarily do. However any other loan where more than £100 was paid by credit card, would likely restore this safeguard.
Flight training can often result in a situation where the student may be unhappy with the provider (for any number of reasonable or unreasonable factors,) it should be a concern if the loan contract ties them into only one school, or possibly another school operating the same scheme.
It may be an entirely suitable vehicle for some people. In some cases it may also prove to be a competitive rate in their personal circumstances. However (and rather like store gift vouchers,) it appears to do little that the untied cash provision of any other unsecured loan wouldn't do, with the latter seemingly providing a wider range of flexibility and options.
caveat emptor!