When I looked at their web page last time, I figured that they'd answered the issue (compatibility with standard devices) in a quite clever fashion. Their devices attach to their boxes using their proprietary anchors. But the devices themselves attach to the anchors using standard screws on standard spacing. So if at install you want to use some device that they don't sell, you can just attach anchors to it, and if in the future the home owner wants to replace devices with standard devices, they can do that.
Their FAQ indicates that you can use standard devices, replace their special devices with standard devices, and even get an adapter than lets you use their special face plates with standard devices. http://www.cheetahspeed.com/cheetah_electrician_faq.html
I've not used these...but IMHO pretty clever.