There was some discussion about the distance of the props earlier. I have been testing one unit that has a 10mm shorter distance between the props compared to previous ones. Distance of props is now 35mm measured from tips, 25mm shortest distance in the center of the blades. Also the rear prop is a 10x4.7, instead of 10x3.8 for both. Seems to be working fine with no problems, and the higher pitch prop on the rear increases the total power output a bit (not that I need it in a 94g plane).
I think there was a slight increase in the interference noise when bench testing, caused by the props passing each other so close. However it's not audible in the air. Also the 3D printed gearbox frame in the latest versions seems to dampen high frequency vibrations from transmitting to the plane. The previous carbon fiber frame sounds a bit louder.
I put the printed parts on sale on Shapeways, just in case anyone who has one of the units needs a spare part. Obviously they can also be used to build a similar unit by someone who knows how to make the props etc:
BTW. If anyone is wondering how strong is the printed frame, see (same material):