I've been waiting for these for a while now. Basically, it turns your 70HP Behringer synth (Cat, Model D, Wasp) into a 3U rack synth. I don't know why Thomann refer these as 'Eurorack ears'.
The design is simple - remove two screws from each end cheek on the sides of your synth, add the rack ears and replace the screws. Simple. Well, until you try to mount the thing in your rack. The screw holes are oval, although on my synth there wasn't enough lateral room on the inside of the screwhole. Whether that't the rack ears or my Model D is unknown. It's not the rack though, as it happily contains lots of other 19" rack equipment without issue. I managed to get it in, but a slight adjustment of the size or location of the screwholes in the rack ears would have been nice.
There's also a fundamental design flaw with this, in that the power switch is on the back. So once it's mounted, it's impossible to get to. I leave mine on as it's powered by my power distrubition unit, but adding a front mounted switch would have been useful.
The material is hard and heavy, probably steel - they feel sturdy enough. Anyway, it serves it's purpose - but Behringer missed a trick not offering a front mounted power switch. There's loads of space for it too.