I have had my charger serviced by BBM and KK.
(car now owned by a buddy who lives with me)
1st time was BBM I initially was not to happy because when I got it back it leaked from the main pulley seal which was why I had sent it to them in the first place. When I sent it back they almost did not warranty it because I had removed the pulley to install it easier. They ended up warranting it though because the day I got it I called them because it was leaking when I installed it.
John did make it right though.
I never noticed any diff in boost and when I got it back the 2nd time from BBM the seal had been pinned(I believe thats what they call it when you make two indentations on the metal around the main pulley seal to bring the metal in tighter) sorry if that is unclear I am not to mechanical. It has never leaked though. I was a little weary of BBM after that which is probally why I used KK the second time.
KK only did the service with new strips, klubber and stage2 port. Felt a lil more boost that time. probally from the port. KK was a little more personable and seemed a touch easier to work with.
Both companies are good though. buddy just had engine rebuilt cause of blown head gasket and charger appears to have excess oil in tubes now. So it is decission time again for me as he doesnt know who to go with.