I hadn't heard of them before, but I see my local shop now has them as well. In theory they seem like the perfect deal especially if you're using multiple lenses with different max apertures(higher and lower than f2.8). However they are steep priced compared to the Canon focusing screens. They cost more than 1/3rd of a Canon t2i hereI would almost be crazy enough to say to buy a second t2i with a different focusing screen just for fast lenses
I do mind indeed. With the 50mm prime it's awesome, but with my two other lenses 24-105(mostly used) and 70-200 f4 it's just too dark for my likings. That being said, having AFMA and knowing that my 50mm focuses spot on is easier to work with IMO than a darker viewfinder.