I don't know if this will help, but here goes anyway. Unfortunately I don't own a MP5, although I do have my first roller delayed bolt firearm, a PTR 9KT on order which should arrive hopefully by this weekend. What I have been using isn't really designed for an MP5 but was originally sold for use on ARs, but it's easily adapted to just about rifle or pistol with a Picatinny rail. It's the Caldwell Brass Catcher. It has a mounting clamp that attaches to the Picatinny rail and then a removable metal frame and mesh bag slides on to the mounting clamp to catch the spent brass. The mesh bag can be adjusted to fit the location of the ejection port on a wide range of firearms. I've used on my AR, Sig MPX. Kriss Vector, and CZ Scorpion Micro and it work great.
I know this product isn't the same as the metal brass catcher you are asking about, but if you have a Picatinny rail, this works great and it doesn't require any modifications to the firearm at all.