I used 3 ground schools. The first one went bust just after doing my Tech exams. I went to Bristol Ground school for the Nav exams and found them good.
I also went to Ground Training Services at Bournemouth for the IR theory exams and found them better. I enjoyed the course more at GTS, smaller class size and very knowledgable instructors. If I had to do it again? I'd use GTS. Only my opinion and i'm not saying anything wrong with BGS.