I have a londonfixiebike bolt on rear cog on my single speed / fixed mbt. I run it with brakes off road and also use the same bike for polo and run it brakeless for trick fun when not palying polo. The cog is very high quality in person and has worked flawlessly. It's nice and round so no big issues with changing chain tension. Chainline issues don'e exists for this set up, just tweak with washers. I am using a 135 mm on one single speed disk hub, it's identical to the DMR single speed disk hub but cheaper, same factory I bet. I would buy one of these cogs again and would also use it on a road bike with one of the front hubs on the back with the axel replaced.