My Sono has arrived...

First impressions, it's really nice. Definitely feels more like a £400 rather than a £149 device.

Sounds good on guitar, as you'd expect... Feels latency free to me playing through the built in cab sim. I like being able to play without using a DAW.

I tried my old cheap 303 clone through the valve pre and it adds nice saturation/mild overdrive. My Uno synth sounded better (subjectively) through the pre-amp using the valve too.

I don't think the valve is a gimmick, it may be positive bias but I think that it makes the guitar feel more responsive dynamically, with more controllable grit when you dig in or via the guitar volume knobs.

All in all I'm very happy. It looks nice, feels nice and sounds great. The features suit my requirements nicely too. And it was a bargain and I love a bargain. It was £419 when new so I effectively got £270 added to my bank account, which is what I've convinced myself and therefore it's unchallengeably true.