Ashampoo UnInstaller 15 is on GOTD today, so I thought this might be a good time for a reminder -- often the Only way to put Windows back the way it was before installing whatever app is by restoring an image backup. That's why some folks use VMs [Virtual Machines] and Sandbox software, e.g., Sandboxie. That's Not to say there's anything wrong with Ashampoo's Uninstaller apps, or Revo for that matter. They *may* *sometimes* go a bit further than an apps own uninstaller, and if you let them search &/or clean Windows registry you may get rid of a bit more junk, though at the same time you may also break something, including Windows. Some changes are not easily reversible, while others may be near impossible to undo. Deleting some files and/or registry keys or entries may not always be 100% safe, so an uninstaller app will not even give you that option.
Sometimes an app will use Windows Installer [.msi file] and use that same file for uninstall, but since that file controls the uninstallation process, it's left behind. A 3rd party uninstaller may or may not find that file. Sometimes files are added and registered with Windows, so that afterwards they're effectively a part of Windows. And sometimes files are added that take over whatever functions were previously performed by files that came with Windows. Complicating matters further, software you installed afterwards may now depend on that, so reversing those changes would cause it to also break. The same sort of thing applies to Windows registry, since a software installation routine can rewrite portions of it -- to undo an installation would require restoring registry keys &/or entries that no longer exist.
There really is no perfect [or near perfect] solution. Adding software, even if it's *supposed* to be portable, means accepting some risk, though you can mitigate it by using a VM or Sandbox to at least check out an app before committing your regular copy of Windows. You can accept the fact that installing software changes Windows itself in ways that may well be irreversible, and that the hype used to market uninstalling software is just that, hype, and some of it will be false. You can set a restore point beforehand, though restoration may or may not work. You can perform an image backup, which will work, with the caveat that restoring that backup will reverse Every change made since that backup, so everything from recent emails to any software or updates added later will be gone.
Myself, I use an old app that barely works anymore called InstallWatch Pro in a VM to monitor file changes made during installation. At the same time I use another old app called Regshot2 to record every change made to the registry. That allows me to see if an apps impact on Windows IMHO exceeds its utility -- if it's worth it -- and if I go ahead and add it to may regular copy of Windows, what I'll need to do to fully remove it. But that's admitted overkill.