Famore makes Missouri Star rotary cutters. They have the ball bearings. They are on flash sales often.
A knife sharpener told me, always sharpen a sharp blade and you never will have a dull blade.
I use the Grace vertical sharpener, run the blade through a couple of times before using. I rarely change blades for dullness. The 28 and smaller cutters make more accurate cuts because the smaller blade does not push the fabric forward as much as the bigger blades. Learned this from Pauline from Pauline's World. I use the Clover 28 size by my machine for quick cuts.