I made this tonight since my X-Axis bearings were shot and carving a groove in my rods. My printer is working seemingly better than ever with these in place of the steel on steel bearings they replaced.
I printed these at half the "height" of the originals for now thinking this would decrease friction, but I might have that exactly wrong. Longer bearings may yield less friction since it distributes the load over a larger area. Try for yourself and please let me know what you think.
At first I printed these solid (no split) which would have required me to take apart my whole X-Axis but then it occurred to me to just split them. I pushed my old bearings off to the sides and slipped these in. It's working great.
I've never bought a set of bearings, but these are clearly cheaper and a lot easier to replace than the originals too.
Note: I'd recommend some lubrication between the bearing and the linear rods.