I’m one of the guys who was actually curious about this comparison (U1 vs U1 Mini+S Booster). I have both units and I thought it would be useful to share my experience with the to help potential buyers.
I can safely say to just don’t bother with the U1 Mini, if you have the funds just go for the big brother U1. The difference is so noticeable that it’s not even worth comparing them, the U1 is simply better - better resolution and clarity, wider and deeper stage, blacker background, greater instrument separation, greater refinement...in a nutshell I would say that the U1 makes the U1 Mini sound “strained”.
The U1 Mini+S Booster combo is a serious step up from regular computer streaming and it beats most streamers at the same price range currently available on the market but it can’t hold a candle against its big brother, the U1.
I’ll be putting the combo up for sale in a few days, so that it can find a new home where it will get some love, otherwise it will turn into a great dust collector.