Yup I've got a CP1 on my M4 Sig,,,,,LOVE IT !! Not even hard to get good groupings with it at 100 m even though the X hairs are somewhat fine with out the light on. I used it once ( the M4) for deer hunting sense I was out on the wheeler and that's the only gun that would fit into the saddle gun sheath I borrowed and had no issue on a head shot at 125m on a 130 lb deer. I like them myself.
Only thing I can say is watch out, there's China made knock offs out there that suck. So don't get one off Amazon or someplace like that, they look the same and the paperwork is a direct copy of the original. But I gather they are prone to canted X hairs, if it say's made in China,,it's not a,,,real ,,, CP1 or CP4.
Get it directly from Sig, there Swiss made, otherwise,,,who knows what you'll get??? The true CP1 & CP4's are all Swiss made.
Oh ya, also the China knock off's have a 3.9" eye relief and the True CP1&4's have 5" eye relief.