I also found this site when doing research, I also had contact with NUS and was provided all the information that i requested.
I have parted with the contractors fee and took a gamble as all references and information provided was all given the thumbs up by a solicitor that looked over everything for me, I have been covering a contract now for around 2 months and have been very happy with what have been supplied to me so far, I was accused of being employed direct by them and being a plant which just sums up certain gas engineers outlook on everything.
so my advise is dont believe everything you read on a forum i have been keeping an interesting eye on some of the threads posted since i found this forum and have yet to actually read from anyone who has done any work or contracts for them just people thinking they know.
So for me NUS Have provided my company with what they said they would and have covered work for various clients that they have registered me with.