I have a couple S3X's and have ridden one it for almost 2 winters, the failures are linked to improper shifting. There is a sliding key in the axle that aligns into 3 different slots, but A. it doesn't seem like its very hard B. it is easy to have the key not fully aligned in the proper slot and it will round or break a comer off the key. Once that happens you can have small pieces of metal kicking around in the gears and causing problems. I had to use the second one a month ago as the first just wore out and failed.

I plan on making a key out of A2 at work and maybe flame hardening it so just the surface is hardened a bit, but still retaining some flexibility in the core. and maybe making the key contact area a slight bit smaller to keep the shifting a little easier.

Now I know most people don't have access to Milling equipment, and I would therefore not recommend the hub either. But It is wicked nice for winter commuting, especially where I live in Northern Maine and its icey and snowy from late November to March. But I just purchased a Cargo frame, and after riding that in the snow I don't see the need for fixed anymore, the longer wheelbase is wicked stable!!