The UAS is certainly not just a flying club. It may well have been seen that way a few years ago, but it is now the only place that a prospective pilot can do his/her basic flying training whether they are a graduate or a direct entry pilot straight from school.
Sadly, the UAS gets very, very little funding for its ground branch members, even though (IMHO) they are vital. The UAS does not get any credit for any ground branch members that subsequently join up either. However, it is an excellent way to see if the RAF is for you, have a great time and go flying (even for groundies). So if you want a bit extra cash at uni by all means join the OTC and learn to dig ditches and get cold and wet, or you could stay with your mates in the UAS.
Tonks