C more and OKO are much larger and heavier, made for long guns CQB type work. C more has a grove in it to fall back on should the batteries die but on the other hand the vast majority of people like the OKO better, go to www.ar15.com
and search the OPTICS section in the GENERAL forum, you will find lots of info on both the OKO and C-more.( you will find them on handguns, as a matter of fact they are used a lot in IPSIC... but these are guns with much larger frames)
Dr, Jpoint, Optima, and the one CZ mounts to their CZ75 line ( the name eludes me - fire point or something like that)are nice and small, all look very much alike. The Optimas had a grove in them aldso so that if the batteries failed you were not SOL. You will need to decide what size dot you want Optimas were 2 & 3.5 MOA I think. All four differ in some way from the other, e.g. the DR is metal, and wil not fit onto a Optima mount...
My 2c - I have an Optima on a MKII and so does my shooting buddie, neither of us would ever change, we are always on the hunt for Optimas.