Welcome to aviation!
I don't know if you have realised already but pay scales for junior FOs on turboprops are generally not that great, especially after having funded £45-50,000 of their own money on training. The partial sponsorship being offered by BE, may not be great BUT getting a guaranteed job at the end of it takes the vast majority of risk out of the initial investment.
Try investing £45-50k on training with no guaranteed job at the end! Sorry to say but that makes your concerns seem quite insignificant! If you get partially sponsored, just be grateful that you will get paid a reasonably good salary to fly modern EFIS aircraft. Once you get that all important experience, then you can move on to bigger and better things.