I've had one for a year and a half. I use it practically every day. It's from Healy. I think I paid about $1,500 for it. Besides the sleep, I have used it on my (ex-) mother-in-law. She had some terrible TMJ pain on New Year's Eve a year ago, so I took her to urgent care. While we waited three hours, electricity held her back from excruciating pain.
Another frequency mode is called "Positive Thoughts". It really works. The most striking example was when a friend introduced me to someone she thought I might like, on a Zoom call. At the time I thought, nah, this person is not for me. There was just no chemistry.
Later that day, unrelated to the Zoom call, I put on the "Positive Thoughts" mode. Within 10 minutes, I started thinking fondly about the woman I had met earlier that day. Scary.
Healy also has something called a MagHealy which uses magnetic waves instead of electricity. I haven't tried the MagHealy.
This stuff isn't cheap, but it's an avocation of mine to investigate things that seem "too good to be true" and figure out whether they are. There's lots of evidence that electrical frequencies work. Healy even has FDA approval for use in (drug-free) pain mitigation.
I'd love to try a BEMER PEMF mat, but they're close to $5K. LifeProFitness (whom I trust) is coming out with a PEMF/infrared mat for around $500.
$1500???!!!??? Ouch!!!