Very much insanely expensive and only experimental. The man I met had a team of like five people needed just to set the thing up and calibrate it for his "brain waves" that day (they had to constantly fine tune the neural net he used to control it because the human brain is so plastic it would change every day and become unusable after a couple days) - plus more researchers running the experiments he was doing. The team had a portable supercomputer running the neural net (this thing was maybe a two or three server cabinets on wheels) that they brought around with them. They had a safety managers to make sure the arm didn't hurt anyone and make sure he was medically okay. This was not a device he used around the house, he was an employee of the research lab and using it for experiments was his full time job.

The risks of these devices are also significant: you have to get risky brain surgery to install them and then you might still reject the implants and have to get them removed.

A very limited number of people have these - the lab this guy worked at had I think about a dozen people, all with BMIs installed using different surgery techniques (some had the implants on the areas where the brain met the nerves going to the muscles so the output to the neural net was a more "direct" representation of movement whereas others had implants on motion planning areas on the brain giving a more "high level" output to the neural net). There are several such labs in the world. My best guess is there are less than one hundred BMIs installed on people today, as well as quite a few more on animals.