Over the past decade or so I've read online how these worked and as I recall they generally don't do all that much on badly corroded coins and relics.
I think Nana40 just ordered one and maybe she'll post something soon.
I never tried one on coins but they sure do a great job on cleaning variable capacitors (radio tuners).
In my opinion, the best all-round cleaning machine is a rock tumbler. Just use water and small gravel like used in tropical fish tanks.
For many years now I've cleaned and sold shipwreck cobs, ancient coins, Civil War relics, you name it--and most spent time in a tumbler.
What a tumbler does is very gently removes layer after layer of accumulated corrosion. This was my main tool for cleaning silvered ancient Roman coins.
The tumbler cleans and doesn't ruin the natural color of the coin.
Rule No.1....don't overdo it. Check the coin often. Better too little cleaning than too much.
Some items with nice patinas & detail shouldn't be cleaned at all.
Best to you,
Badge