My experiences of the NAS have been rather mixed. I was a member of their social groups in Bristol and the way that they pulled out when the funding was no longer available was disastrous, they gave us very little notice that it was going to happen and we are still trying to recover from the fallout (18 months later). Not to say that the groups were perfect because the way that they facilitated the groups wasn't brilliant either. They didn't treat their volunteers very well either and have had a lot of complaints from support workers and volunteers alike about the way that they run things.
The outreach service provides my support 8hrs a week and it has it's good and bad sides. They have been chronically understaffed for a long time now, yet I don't see that they are making much effort to improve that situation. As soon as they gain a new member of staff, one leaves! It doesn't help that the pay level is so low that a lot of people are put off doing the job. So they never actually get more staff in. Their communication at times has been shoddy to say the least (support turning up late with no warning, last minute cancellations, incorrect information regarding rota times and so on). They have also been rather good at times as well, trying to accommodate all the things I need to go to so that I have support for the important things. They are slowly improving on the communication side of things and I give feedback regularly. They have definitely improved in the 3 years that I have been using them. My alternatives to NAS support would be Brandon Trust (Learning Disabilities) or Second Step (Mental Health), neither of them I've heard particularly good things about locally.
So yeah mixed experience with them really.