Splinter,
The ones I use are the ones from Chef Specialities (chefpepper.com). They are the same ones that Woodcraft, Woodturners Catalog and others sell. The reason I use them is availability and price. I few years ago CS would sell them at wholesale to WW'er mill makers. Soon after they became available at retail through Woodcraft and others they stopped. Those of us that were existing customers were grandfathered and are able to continue at the wholesale price. Because of that price advantage I haven't tryed others. Really, the only other common mechanism out there is the crush grind ones. The mills with the highest regard and acclaim is the ones with Puegot mech's. I just don't know how to get them in this country.
Rob