I have no personal experience of other filters as I did my research and settled on B&W's MRC range as the best available. But I already have two of these to protect my L lenses and have never noticed any degredation in image quality - the one time my shots suffered from image flare from long exposures at night at f/22 (not unusual even with the best lenses) I removed the filter and it made no difference.
Also, I had one of the non-MRC filters fitted to my Canon 24-70 f/2.8L lens when it took a tumble while on holiday - I was trying to pack for home but had barely recovered from a burning fever of some sort so wasn't thinking properly. My camera, with lens attached, took a tumble onto a wooden floor - the filter smashed and was bent, but other than the smallest of scratches on the outer element of my lens from the broken filter glass, there wasn't a mark on my lens. I took it to a specialist to remove the bent filter and have the lens mechanism checked out and a year later the lens hasn't missed a beat.
Without the filter attached this could have been VERY expensive. Even if insured (I am), the cost of this filter is less than most insurance excesses, and besides, if your lens takes a knock with this fitted you won't miss out on shots while your lens is fixed.
Note, though, that stacking this filter with others, say polarisers, can cause vignetting on the wide end of zoom lenses. Changing filters is difficult though as you end up juggling with lots of bits of glass. I am about to muy a third filter for my latest lens and had wondered about one of B+W's slim models but at nearly twice the price I don't think they're good value.
Some people don't like filters for protection but I think they're worth it - the best ones shouldn't degrade image quality at all. But don't buy an expensive lens and then stick a cheap filter on it; that makes no sense. Spend a few quid more and get this. You won't regret it.