I bought a set 43 years ago. Set them up in the carport. A bit scary at first, but you get very smooth, fast. Great for leg speed. I took a while to be calm enough to shift with downtube shifters! A track bike is actually easier.
My first use ended up with me riding off the side, fortunately the non belt side. Then rode directly up and down the street. I could not believe how I could do jumps off the saddle and the bike was not moving around side to side.
Very good for form.
They get boring though.
Never became comfortable enough to ride no hands, I think to do that there was a trick of setting up the front roller in relation to the front axle center, no one would tell the secret.