It looks nice dont it lol. Mine sits at the bottom of my tester bag and has never been used. Think its for IR testing with the botton on for one handed operation. Might be wrong tho so await others response .. Andy knows the answer to this and this has come up before on here. HTH
Isn't it for use when live testing so you don't have to grow a third arm to press the test button on the instrument whilst holding the probes on the terminals?
Yep, it can be useful, I've used it for RCBO testing aswell, or any measurement that requires the test button. But gotta be honest most of the time it stays curled up at the bottom of the case!