I think the issue with after-market Android infotainment units is not that they do not work, but that without having specific brand names to go by, it is impossible to tell if that Chinese unit going cheap on eBay is actually good, or perhaps it will preform poorly, then overheat and blow a fuse etc.
There is also the issue of full integration with the steering wheel controls, instrument cluster display, and other car systems (where applicable) e.g. memory seats, heater fan controls, etc.
But this is something most owners will probably be willing to live with if it means they get a good system that cost half as much as COMAND and is more flexible in terms of the software it can run.
Again - the issue is knowing which one to buy and which one to avoid....
PS - I had COMAND retrofitted to both my current and previous cars mainly because I wanted the original OEM look and feel, as well as the integration with the rest of the car, and this is how I prefer it, but I do accept that having an Android-based system is a more flexible solution.