Solid built quality, more than enough power for my speakers (Mission LX-2), and handy meters to make sure you are using a correct gain staging so that you don't push it unless you have to (as pushing an amp towards its upper limit might not do well to the speakers' tweeters).
I bought both this and the T.Amp E-400 for my speakers. The E-400 sounds a bit bigger, the soundstage is a bit larger, it's deeper but with a bit less clarity. I kept the S100 Mk2 because it's smaller, it has meters, no fan, and has a bit more clarity. It was a decision based on my job as a mixing engineer. I need something as revealing as possible. If I needed the amp just for listening I would probably get the E-400 as it's a bit more pleasing and less analytic, but I found the S100 clearer. Part of that is that it is brighter compared to the E-400, so you might want to consider it based on the signature sound of your speakers.