As I am doing CPL(H) ground exams and there are only currently two providers for this distance learning course, I can't comment on Bristol but their reputation appears to be very good from other posts on this forum.
As a helicopter, I am in a very different position to anyone wanting to go into the airlines with regards to hour building (I'm nearly there anyway!) since my career ambitions are quite different and my hour building has been based accordingly.
I would certainly recommend you stay with one school so make your choice wisely! Is this for the flying training or ground school? Either way, I would stay with the same one unless things really go pear-shaped!
Cheers
Whirls