I was genuinely impressed about the built quality as soon as I took it out of the box. The sound quality is really impressive, even before considering the price. I am giving 4 stars to the features just because there is not meter, which you can find in some other T.Amp models. The fan is quite noisy, so if it is for a quiet studio environment you might want to disconnect it (probably worth checking the warranty though!). I returned it because I had both this and the S100 Mk2 for my Mission LX2 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 if I didn't order the S100 as well, the E-400 would have been perfect anyway (but I would have disconnected the fan).