TU3 works on the basis that it snapshots file locations and the whole registry before and after (actually it can be used for any app that runs on your system - you decide when to take the before and after snapshots). Using it to uninstall then undoes all the file and registry changes.
This only really works if you haven't installed something since that changes the same file locations (eg. file associations).
The other thing I have found is that if other apps are running at the same time they will also make some registry changes and so the uninstall routine could have unwanted consequences.
One useful thing is that you can edit the unistall data set - so you can make just the changes YOU want.
I don't personally think any of these uninstall monitoring packages should be used in any automatic way. They are a useful aid ...
Another really useful thing they do is to show you what changes are made for time limited trial software ..... I leave it up to the imagination what potential this may have