Why would you want a company to have all your money anyway, even if it is safe in escrow? What if you decide that another provider is better for you? It happens, it happens to even good schools chosen carefully.
I've met people who have changed from prominent schools in the middle of CPL courses. I know someone who went to a school I have heard to be very good, that I would happily recommend on the strength of the reports of people I trust and about which I have never seen a bad comment here. My friend is not satisfied and is considering changing FTOs for the IR. How could you do that if you have signed an agreement and handed over your money to joint control? Even if you manage, the legal wrangle could drastically delay your training (with a loss of some of the money, I have seen up to 25% of contracted training costs).
If there are places that will offer you a course where you pay for the flying you are about to do, or even that you have done, you can keep control of your own training. You are the one who can best judge your requirements, you can make sure the FTO listens to them. The schools should be looking to keep you satisfied at every stage to get your next pound (or £330 as the case may be
), rather than looking at you complacently as a completed deal.