We have published a White Paper on The Hidden Costs of Homegrown Updaters to help everyone understand the range of costs to build a feature-complete software update mechanism for your IoT devices. As more and more embedded systems are coming online, basic capabilities such as the ability to update and patch them are being overlooked and don't take into consideration certain risks, which we detail in the White Paper.
We have also published a Requirements Checklist for OTA Updaters which provides a comprehensive overview of what an OTA solution should have.