I can tell you about the UAS.
The UAS is RAFVR and is primarily for pilots. About 20 are recruited every year and the idea is that with no obligation on either part, the student can get an idea of the RAF life and career, and the RAF can get to pick and choose. All UAS cadets have to go to OASC like anyone else to get a comission and their time on the UAS is under constant scrutiny, so by no means an easy ride!!
Hope that helps some.