Couple things I did not mention in the UberTuber doc:
It's voiced fairly warm and smooth keeping in the spirit of the tube design. However, some may like more treble and this is easy to do:
Make C5 470pF (either ceramic or Mica) instead of 100pF and C8 4n7 instead of 10n. You can socket these for experimentation but keep in mind that if you are using Mica for C5 it won't fit in the socket - leads are too fat.
The Boost switch may pop the first time you toggle it. You can prevent this by toggling the switch one time when you first power up with the pedal off. I should have included a drain resistor there but I simply forgot. If you want to do this, put a 1M resistor between the two switch lugs like this. This gives the cap a path to ground while the switch is off and then shorts the resistor when the switch is flipped.
I gotta build one of these. I have a few sub-minis just collecting dust.