I can't say much about the macOS market, but I do know that MDM-style APIs are practically the only way to write a third party control app for mobile devices. With the way Apple is moving macOS more and more towards their control, this may happen on the desktop in the future as well.

Schools also tend to use MDMs, but often in combination with Chromebooks which don't typically run third party software anyway.

I mean, “many” people use SaaS apps which utilize MDM on end user devices, but many parents I know who are in tech roll their own to filter the net for their kids devices and (to a much lesser extent) monitor them proactively.