Yeah, as has been said, the device is an Arm Blaster (also known as the thing that makes you curl exactly opposite of the pic above. I guess Arnold decided to reduce the weight and focus on technique, ha.)
It's an okay tool... until you have the strap break in the middle of a set. Been there, barely survived. That wasn't any kind of fun.
So, yeah, I generally advise against them due to the chance of injury if they break. If you want super-strict curls, do them against the wall and keep your head, shoulders, elbows, and tailbone touching the wall for the duration.