Never used one in 50 years, can't say I even saw or heard of one being used for most of that time either, seems to be recent audiophoolery. Can't imagine it helping a tt maintain speed either unless it's a pretty poor tt, might even stress some designs (like direct drive). If you really have a bunch of warped records you must play perhaps a clamp might be better, but better just not to bother with warped records IMO.