My wife and I both have a MT500 ‘spray baggies’ (had ’em over a year), the ones she’s got have been great, have worn well and the ar*e panel has stayed waterproof. Mine on the other hand – the first pair leaked badly after 2 rides, so replaced by LBS for another pair – which also leaked from new. I noticed yesterday that one of the seams has now worn through.
So, IMO, a good concept, but sadly it’s the usual Endura hit & miss quality (seems to have got worse since production went to China – er…what a surprise!)
If it’s any help, I think Altura do a clone of the spray baggies – dunno if quality is any better tho.