Another question you might ask, is how long they have had the discount prepaid scheme for?
If it's only rencently introduced, it's likely it was introduced to help solve a cash flow problem, and is indicitive of impending problems.
If it's being going for a number of years, then that might not be the case.
My advice would be to be very careful. Why would they want your money in advance? It must be to help solve their cash flow.
dp