UL (Underwriters Laboratories) approval is a good thing when no other guarantee of standards is available. It doesn't automatically mean that a product which receives the certification is better than one which does not seek it. UL is one independent testing company, there are others and an audio specific one is THX. These are pay for certification companies. Just because a product does not bear one of their logos does not mean that it will not pass their tests. Many products exceed them without ever paying for the certification. Some Bryston products have been THX certified. Whether a Bryston amp bears a THX logo or not, I'd be more impressed with the Bryston logo than the THX logo. In my experience, THX in itself has not proven to be the most telling badge of quality and performance. Further, Bryston products sold in Europe must meet their CE requirements.
-Bill