They speed up my set-up/pack-up for mobile DJ work.
The clamp is robust, though the large plastic handle sticks out a bit, which can be awkward when packing away speaker stands with them still attached. I'd prefer something that had more of a wing-nut shape rather than a single arm design.
The spring-loaded fastener works well, and often I don't bother to even tighten the safety clamp to stop the light moving - the clamp will hold it in place, just make sure that it's clicked into place.
It fits well onto my standard speaker stands, and once you get the hang of slotting the bolt into the socket (it needs to go in straight) then you'll find it a real time-saver.
Quite expensive, but will probably last a long time, and build quality is good.