Marble's also makes an excellent fiber optic sight for the GP-Redhawk-SRH, in orange and green.
I also have the Hi-Viz, and it's brighter than the Marble's, but the Marble's is non-interchangeable and tougher for field-CC use.
The Marble's also comes in a bunch of different sight heights for different guns, bullet weights, etc. Midway must have like 20 different kinds of them. I bought the lowest one, for the .480 SRH and used it on my 6" GP100 with no issues.
I just didn't like that the "dot" was half obscured by the bottom of the rear sight blade when I took a sight picture. I am 6' 4" with long arms, so this may explain why the fiber optic picture doesn't quite work for me, unless I alter my hold and bend my elbows so I can see the entire dot. Then it works fine, but I shoot with my arms extended.
I since replaced the fiber optics on that 6" GP100 with a set of the XS "Big Dot" sights. Works great for my intended purpose, which is a dedicated HD and "around the property" gun since Black Bears can get aggressive around here but don't get too big, so .357 is more than enough. These sights are for short range hunting (hog guns) and "fighting guns", I can make rapid hits on a silhouette out to 50 yards, not with target precision, but center mass hits. These aren't Bullseye sights but they are FAST! They seem out of place on a 6" full lug GP100 but for me they work. I also wanted the recoil control of the full lug and the extra velocity of the 6" barrel for the .38 +P's I use for HD.