I was forced to cut out the diamond pattern from both sides of my 12 X 12 filter because my furnace was being starved of return air. I tried the 13 to 8 Mer first but was unable to tolerate the loud noise coming from registers.
The quality of the filters seemed to be OK, but they are slightly smaller than any other filter that I have and when the return section starts, the filter is sucked back up into the box area, and it causes a very loud snap.