You're probably on the wrong forum for this but I'll try and answer your question..
I can't speak for the specific software you have mentioned, but theres no reason why they shouldn't do what they say - to a point. They work by scanning your filesystem/registry for any references to the application you are trying to uninstall and deleting them. You can't be sure they have caught everything though.
The best thing to do is to use an applications bundled uninstaller (if it has one) which knows exactly what has been installed where and exactly what to remove. If the software you're trying to remove is malware/spyware and comes with an uninstaller, then you can be pretty much certain that the bundled uninstaller is just a 'front' and will leave any malicious components behind - In this case anti virus software, or in the worst case a full system rebuild is required!