I have not tested this application at all. Still, the AVG folks are reliable and don't ever seem to release untested or overly buggy stuff, so it's probably worth downloading and testing.
Rootkits are, after all, a growing menace. They often go undetected by anti-virus or other anti-malware applications because their signatures have not appeared in the wild before and so are not included in the application's signature database, against which it compares executable code to detect virii, etc. This application may be just what we need for anti-rootkit protection.