In Canada, they are illegal, but the reality is that it is very improbable that anyone would get shocked. It is mainly UL making money. The EU probably also makes them illegal. They are responsible for the crappy binding posts with plastic covers. Apparently they thought someone would plug and ac cord into the amp binding post banana holes. It probably would be best to get such people out of the gene pool.
If you have a Tripoint grounding unit or the Entreq grounding unit, I doubt if you would get any benefit from lifting all grounds except the preamp, but without those units, I have always found great benefit, if you have good cheaters. Siltech used to make very nice ones but no longer. Synergistic Research at least used to take the cheap, gray cheaters you can get at Lowes or Home Depot and zap them on the Tesla coil. I had both and the zapped ones were clearly superior.
I am not using them with the HFC cables because the wall plugs fall out with the cheaters between them and the wall outlet.