The simple fact is that if you pay upfront, you run the risk of losing the whole lot.
Flying schools are possibly the least stable businesses around.
Paying upfront is frankly mental.
When I put invoices into flying schools, there is no delay, I've seen too many of them go to the wall and take many people's money with them. I have no intention of letting mine join that horrid club.
But hey, you want to take the risk, go ahead. Personally as someone who's been around flying schools for a few years. I think you're nuts.