The foambymail stuff is ok, but much lighter than auralex. Apparently they don't even hold up to their specs. So they are fine if you are on a really small budget or really don't want a lot of absorption. Maybe fine for gobos or for more lively space. On a budget though you are way better off going with DIY 703 or Rockwool treatment.
But I digress... I did notice a big difference when I got the MoPAD's. But my monitors sit on 4 space racks. I could actually hear the rack resonating which the MoPAD's stopped. Some have claimed you loose some bass, which might be true, but it will be more accurate bass. Ideally you want your monitors on stands, but it doesn't always quite work out ergonomically.
If you actually call sweetwater or full compass or some place like that, you can actually get the MoPAD's cheaper. I don't think it would be worth the time to A/B them or something. That would cost more than the extra $30 for the MoPads.