The owner sent me a prototype last year to try out.
My initial results were inconclusive as to its effectiveness. I may try it again this year though.
Installing the metal strips were not that easy. I didn't want to permanently nail them to a deep box (since I was just trying it out). You can't secure them to a bottom board either. The metal shims need to be on all 4 sides of the box, and the two that go on the shorter sides of the box (front and back) are shorter than the length of the board, meaning that the ones on the sides extend all the way, but the ones on the front don't overlap. This results in having the front metal strip just fall down, unless you secure it to the top box. I just added two wooden blocks to act as "wedges" to hold the front one in place, and that appeared to work alright as a temporary measure. If I wanted something more permanent, I'd nail them to the box.
The strips on the front and back also weren't quite long enough. They left about a 1 or 1.5 mm gap between the metal strips on the side and the metal strip on the back. Probably wide enough for a beetle to pass through. The designer thought this was weird, as it fit perfectly on his hives (mine were Mann Lake). He may have fixed it. Or mine were oddly too wide. I don't know.
As far as effectiveness goes, about 2 months after I installed the strips the hive absconded (most likely from robbing pressure during a dearth, although I can't say for certain). During those 2 months, I noticed only a few beetles. Less than some of the other hives had, but I can't say a statistically significant amount less. The beetles that were in there could have been in there since the install, or they could have gotten through the 1.5mm gap, or the beetle rim could have failed and the beetles were kept low because the bees chased them out. Who knows.
You can probably build your own for a heck of a lot less than they are selling for now ($16.00 on the Beetle Baffle website). I'm not a metal worker, but I would imagine it would cost you a dollars worth of tin or other metal, assuming you couldn't use scraps. Originally the owner wasn't willing to share any photos for fear of having someone duplicate his idea, and for good reason. He filed his patent, which is why you can see photos of it now. It's patent pending, which doesn't really mean anything. The patent could get approved, or it could be rejected.
As far as the extra space goes, I doubt it would be a problem. I never have an issue with vent boards, and sometimes bottom boards are too wide, or I put a medium frame in a deep box. They rarely attach comb to the bottom.
Hope that helps.