The problem is that if you click the obvious "install this script", button without tamper monkey installed, on the script page chrome tries to install the script as a extension and it is not allowed. There is not information that tamper monkey is needed.
If you click there with tamper monkey install the script will be installed in tamper monkey
My understanding is that extensions in chrome can just be java script files without any need for tamer monkey but they have to be installed from the web store. (Or i have miss under stand it)
This script will obvious not like that because it need tamper monkey