i have a customized SlikStik Classic on order.
i started out with a CO2-based design, but ended up concluding that, when just one player is playing, you end up pretty far off-center much of the time. i tried some custom layouts, but kept focusing on the center of the panel and ignoring the periphery, so i scaled back to the Classic size. i may some day design a CO2 as a "2-player-only" panel, a job i think it could do very well.
another application that i think the CO2 could excel at would be the "coffee table" or "pedestal" panel, which is not rigidly attached to a cabinet. then you could just slide the panel right or left, to use off-center controls, while still being centered in front of the monitor. in fact, my inital use will be in this mode, but i designed my panel to be attached to a cabinet eventually.
i would give you the same advice as is given to people doing their own custom layouts: make a full-size print-out or mock-up and see how it feels. keep on "test driving" designs until you're confident you'll be able to play all the games you want to play comfortably. i found many problems this way. since i don't yet have my panel, only time will tell if my panel works out the way i hope, but i'm pretty confident...
you can see some of the thought process i went through
here.