I did Module One with them recently, now doing Module Two, can't recommend them highly enough. The study materials are top notch, fantastic back up during the distance learning phase is available, and the brush up course whilst certainly hard work clarifies and consolidates all the learning really well, the instructors are fantastic and certainly know their stuff. The feedback questions you get at Bristol are also extremely helpful. The whole experience would have been a whole lot more stressful for me had I not had Bristol's expertise behind me, and no I promise I don't work for Bristol groundschool!!!
Also worth mentioning I went to Bristol based on my instructor's recommendations, who acted on HIS instructor's recommendation, and if I ever become an instructor I will certainly be recommending it as well!!