I've used it sometimes...
The problem is that it does not 'work' for applications that requires a reboot to install. About these installations I'm much more afraid than the ones that does not require a restart (generally not adding low level drivers, services, etc.). RevoUninstall does the job for the applications that does not need to restart after installation.
Anyway, Returnil is a good application for testing or letting the system partition clean. I have installed avast is a second partition, as all other programs that requires updates, so I can use Returnil and update my system regularly if I need to use it.