They work if you have minor long warp but like those overpriced "flattening machines" don't expect tight warps to be helped.I haven't tried a clamp but from what I read it would be last thing I'd get from VPI who make a good one.Yes if you use a clamp (I use best which is a carbon fibre) you can over tighten and record will slightly be pressed up from center but it's minor.It's good on other hand to have as much vibe isolation as possible so it's good in theory but for how much price?And VPI fits snuggly on platter so does not have to be centered.You need center guide touching you wax (so must be used carefully or padded) to get to work right.And in and what if you drop it and damge the $2K arm,the $2K Blue Note opriginal,or the scratch the $2K (well $5K) deck?I have read and thought about benefits but will for now keep my better TNT5 methcrylyte/lead platter rather than get a $1200 upgrade that fits ring and put $$$ elsewhere.I see some being sold off because people just don't think it's worth money that could be spent on rack,isolation or better cart,arm,platter or phono stage (or in my case better feet or finally getting Gingko/VPI feet).And if I needed to use centering device I would just say not worth it at all.Now let a user say "he who hasn't used doesn't know" but I have studied it a bit.
Chazz
Chazz