I have the HS503C on my soon to be SBR'd Scorpion.
I have put it on another SBR'd Scorpion at my LGS, and I really like it. I didn't use the provided AR riser, and it makes a nice, small & low optic for the CZ.
I really like the Circle Dot, but it's easy to switch to just a dot for those that prefer that option.
Hope this helps,
Bob S.