My experience of BGS was that the course notes were good. I rarely used the computer program, except for progress tests, and some of the more complex diagrams.
Still, I did struggle with some subjects, and had to buy other books to supplement the course notes.
Their feedback was good, except AGK which was a shambles.
The class sizes were huge - my Mod 1 was about 30 people. Mod 2 about 15.
The instructors were good, friendly and new their subject matter very well.
If I wanted smaller class sizes and a more intimate environment, I would have looked elsewhere. Looking back on it now, I would probably have looked closer at another school.
I did visit the school and chatted to students who were there, including the CGI. I tried to visit Oxford at the same time, but they couldn't fit me in on the week I had available. I also visited Cranfield, and met with CCAT and the other school on the airfield. This shortlist was gained from visiting the Flyer show at LHR and also from advice taken here and from my flying club.
GTS were not around when I was looking, but I've heard some good stories about them, and they have smaller class sizes too. There's another new school full of ex-Oxford instructors, but I don't know anything about their quality.