When you download the zip, right click and select properties, and on the General tab click the "Unblock" button. Otherwise the files will be tagged as coming from the internet and Visual Studio will refuse to load them.
You can just put the dll and .AddIn file in the \Visual Studio 2010\AddIns folder and it should work.
To remove/uninstall the AddIn, normally you can just delete the two files from the AddIns folder.
More here: http://msdn.microsoft.com/en-us/library/ms228765.aspx
One reported incompatibility is if you have the flag <NetFx40_LegacySecurityPolicy enabled="true"/> in devenv.config. You must remove it for the addin to work.
If you want to customize the AddIn, here are useful links for AddIn programming: