On Android, it's still much easier to install apps from outside Google's app store (just change the "install unknown apps" setting, download the .apk file, and open it) than it is on iOS.
Apple has earned plenty of criticism themselves, but I do appreciate that they curate the app store with humans.
For iOS your users will have to sign it themselves (but still via Apple, who could block that too) with their own developer account, just to get a time-limited install. Or, even worse, use a jailbroken device to work around all this.