I have used this brake on my fixed gear commuter bike since september 2021 and it has worked great. I do not recommend this for serious cycling (mountain bike or road cycling) but for commuting it is perfectly fine.
Printing instructions:
Print with as many perimeters as possible (I used 7 with a 0.5mm nozzle).
I printed everything in PLA. I recommend a to use your strongest filament. Choose filament that is not so brittle.
Does not require any supports when printed in the orientation of the picture below (also included in the print profile):
Required hardware:
14mm M5 bolt + normal nut (for the clamp)
30mm M4 bolt + nyloc nut (for the lever)
(Optional) small M3 screw for reach adjustment
Assemble by placing the M5 nut in the slot before sliding the clamp over the handlebars.