All in one systems aren't all that bad as long as they are quality and you can replace the sensors. I program control systems that integrate EVERYTHING in a home (lighting, shades, hvac, access control, distributed audio and video, pool/spa, etc.) and it's all tied to a single control system. If the system goes down the home owners have extremely limited control (lighting only from physical switches and hvac only from thermostats) but the systems are usually rock solid. Some clients will fork out the cash for a second control system to stand by for redundancy but very few do.