To be fair, just about every brand of rigid permanent filter is slightly smaller than the filter size it replaces, and this is no exception. I replaced a mid-grade disposable 3M filter, and this was not exactly the same size, this was about 1/8th smaller. That's because cardboard filters can be forced and squeezed into slightly too small openings (if you have one), whereas rigid or semi-rigid aluminum (this is aluminum) or plastic won't, so almost all of them are a bit smaller than the exact size. They have to make a choice, and almost all rigid filters are a bit smaller than their cardboard counterparts. It's up to us to make up that difference.
In my case, the slight difference in size left a gap where air could completely bypass the filter on one of the four sides of the filter. I used weatherstripping with one sticky side to make my 12 by 12 fit. Overall, that does the job, but I do have to take it out and add a little more weatherstripping. How well will the weatherstripping survive a cleaning, remains to be seen. I may end up taking the old cardboard filter, carefully cutting out the filter, leaving the cardboard frame, and using both.
As far as perceived quality, it seems good.