The main concerns with this scheme appear to be:
1) The exact terms of employment
2) Being dropped by qatar at some point before achieving 1500 hours
Compared with the EasyJet MPL and BA FPP there is very little precise information on exactly what the terms of your employment would be at the end. If this is yet to be clarified then that is acceptable but I agree that it would be very unwise to part with £105,000 without finding out exactly what your salary and terms would be.
Secondly people on here have suggested that Qatar have been very intolerant of any mistakes made by pilots and are quick to sack people for various things (only what I have read, no personal knowledge). This would be quite a concern as a sacking before you have accrued 1500 hours would leave you with nowhere to go, nontransferable licence and a large debt.