Brake - love it. My last 15 trials bikes have had rear disc. There is no pad wobble when set up correctly, but there is some spoke flex. I'm used to it but it's personal preference.
Yes, you need to make the guard over 180 degrees so it clips on.
Freewheel was taken off since there is a problem that becomes apparent when the freewheel is used 'for real' that isn't evident on the test rig. Rockman are looking into it and the freewheels have been taken off sale until it's sorted. I should have a new sample in the next week or so to try.
Rear hub also bust - however nothing to do with the bits that we thought might break! The fibreglass inner layer was too soft and deformed, so the hub started creaking and it was really annoying. The carbon was intact and the glue held well, but I had to destroy it to remove the flanges. Got another centre piece curing at the moment made of 100% carbon, hoping my freezer will be cold enough to shrink the mandrel to release it...