Prefolds get some bad press i think, but are a pretty decent nappy system, especially when you take into account the price. The prefolds themselves are also very hardwearing and will last and last, easily more than one baby.
They are only as good as the wraps you use though as (unless you plan to fold and nippa) the wrap leg elastic is often all that stands in the way of a blow out - especially on breastfed babies. And like PP said, Bambino Mio wraps are pretty hopeless (imho). Much better are Mother-ease, or for pretty try Bummis or Thirsties Duo. You will also usually need to boost with a doubler as baby gets older, which can make them bulkier.
If you do fancy trying them I would recommend picking up a couple and a nice wrap pre-loved and seeing how you get on with them once bean comes along. £22 is cheap but loads of pre-folds around pre-loved (especially B.Mio) and you wont get £22 back if you dont like them. I keep a prefold and a wrap in the car boot as an emergency "get us home" nappy, so even if you dont like them you wont have wasted your money.