Mike, All I can say is that it handles my UWA 14 mm O.K. It does not "lock" at all, but there is added resistance because of the belt. You can still manually focus, as the belt just slips over the pulley.
Don't forget to make a "belt keeper", which stops you "losing it" in the grass, & we wouldn't want that now, would we? (If the belt breaks simply wind the new belt thru the open coils.) See attached.
HTH.
L.