I own a 4B ST; great value for money product. Great low end, good dynamics,neutral without being cold, built to last a life time, and a perfect match for my PMC speakers. However you need careful pre-amp pairing to smoothen out the upper mids/ lower highs.
What really sets Bryston apart however is the people behind it; their service sets a bench mark for other companies; send them an email and the VP will get back to you in a matter of a few hours; 24/7. The twenty year warranty is no joke; mine had a problem after being hooked to a speaker with loose wiring. They fully seviced the amp free of charge and shipped it back long distance as well.
Shortcomings: not the most refined upper mids/ lower highs, sound stage could have more depth. I belive the SST series corrects those faults though. Overall a highly recommended product.