It isn't sturdy enough to grip a guitar body, clamps should be much more rigid than this. The tiny litte screw to adjust the length falls out all the time, and is difficult to find again.
The 'rubber' (which looks more like plastic) is smooth and curved, probably the opposite of a good design for something that relies on friction... minimal surface area. Also it fell off soon after I opened the box, so I had to glue it back on.
It is very probable that you will knock it off the clamp and the mic will break, I recommend generous application of duct tape.
If Thomann made a metal version that was reliable I would pay £20-30 for it, because the mic is still worth having.