I've had the 281 for a while now and have enjoyed it quite a bit. The XLR out to my ear is a lot more enjoyable than the single ended out which is more flat/thick in comparison. For me, part of the charm to the amp is it's size, for what it does it isn't huge and only weighs like 13 LBS, so I can travel with it easily. I know that not important to most people since it will just sit on a desk.
I have noticed DAC pairing with it is quite important, as my EAD DSP 7000 sounds the best with it, better than my Progeny and I even prefer it over the Theta Gen V at times.
I haven't heard any of the other models, but I do love the 281 for what it does, and despite the weird db switches in the back, it turns it into a very versatile piece of gear.