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 betterThis is likely true if you take the "stock" U1 Mini and compare it to the standard U1.
That being said, I took a close look. I think the U1 Mini + Sbooster is probably going to be equal to the standard U1 if you just use them as a digital transport.
The only thing that the standard U1 has here is a DAC and analog output. If you don't need this and are still intending to do the Sbooster mod on the U1 MIni, then I would say go for the U1 Mini. The digital transport section is the same on both.