There seem to be a few slightly confusing statements in the manual install instructions ((- BROKEN LINK -)
If in future you choose to upgrade to a new version via installer or a newer zip package, make sure you remove ALL the installed files from the previous version first, then perform steps 3 and 4 (running devenv /setup) in order to reset Visual Studio's extension cache.
This should probably be "step 4 to 7".
If you wish to remove NCrunch, you need to delete the installed files and then also perform steps 3 and 4 again.
This should probably be "step 5 to 7" (I doubt you mean that to uninstall, you need the Remco Software directory to be filled with the contents of a new ZIP.
On the download page of the product, it says:
(Requires manual installation. For troubleshooting only)
For 2017, this is the only way to install it whenever you have more than one side-by-side installation of Visual Studio 2017, which becomes more common nowadays. In other words, not "only for troubleshooting".
And one suggestion
From VS 2017 15.2 onwards (the RTM is at 15.4 I believe), vswhere.exe is part of the Common Tools (see https://github.com/Microsoft/vswhere). This makes it much easier to automate the ZIP-installation with a batch script. Since I am bound to have to repeat this manual process quite often (as long as there's no way to install NCrunch on side-by-side installations), I will try to look into this. It may help others, too. The most recent version of vswhere.exe includes my proposed fix to find an installation by its nickname (see https://github.com/Microsoft/vswhere/issues/104).