yes, those are the ones, have you ever used them. i always thought the grip would slip out of place during use, causing possible wrist injury.
Yes, I used them years ago at my original gym, which is the only facility I've known to have them. Some of the veterans there called it the geode bar. We had a plate-loaded barbell one, and a cable attachment version.
I don't think they're dangerous. They do take some getting used to, though. The handles do not lock into position, but are meant to rotate to allow for adjusting supination/pronation
during the movement, almost offering the benefits of dumbbells, but with the stability of a barbell.
Imagine doing bilateral Zottman curls with a barbell. That ability is the principle behind this bar.
It is an obscure piece of training equipment, for sure.