One other thing I didn't mention is a motor shaft which has a pronounced flat spot makes it very difficult to get a true rotor mount unless the collet/screw arrangement is machined expressly for that motor shaft. I had real headaches trying to adapt the "ammo" line of inrunners to grub screw type mounts because they simply wouldn't run true in any configuration I tried. If you're a machinist, you can deal with stuff like that by making custom shims or collets, but most people can't.

I don't blame you for passing. Unless you really love tinkering with these things, and want to squeeze every last drop of performance out of them, home grown dynamic balancing isn't worth the effort IMO.