I can see how that'd happen. My mother for example would have probably been slow to adjust to something like the Ecobee/Nest, but she always tried...but yeah, if something got unexpectedly changed it could be a problem.
That said, there ARE lockdowns that can be put in place on the Ecobee where you can lockout things with a password, so you can prevent unintended changes or whatnot, while leaving basic functionality (temp up/down) accessible. That could be an option to prevent unintended things from happening.
The other thing to keep in mind if you are installing this for an older non-techy family member is that you can setup the remote access to it and then fix or adjust things from your own house (from your computer or smartphone) for them - no home visit necessary.