Furutech / Air Tight LP Flattener - do they work?

I have the ring clamp and heavy platter and I like them both. I disagree that the ring clamp is really cumbersome to use. It works very well on dished LPs. Of course, it can do very little for "rippling" warps. The disc flattener would be better for that but I think if you get the occasional rippled record, it's more cost effective just to find another copy than to spend big bucks on a disc flattener.

I have the HRX with outer ring for several years now. Works very well and there are no issues whatsoever with damaging your cartridge. You will need space or a stool or something that you can rest your ouiter ring onto when changing records.

I also have the disc flattener and that is excellent as well. However generally when you pull out one of your records you want to play it then and there. You can then flatten it as it takes several hours in total.

Ultimately it is better to flatten the record. After you have done that therer are no issues on whatever table you play with

Both, in that the clamp and ring combo improve the sound significantly even with flat records, and, as noted above, they will not cure severe edge warps.

Are the vacuum platters turntables like Basis effective for severely dished LP's ?

Are the vacuum platters turntables like Basis effective for severely dished LP's ?

Yes