Reinstalling the Addon Manager is totally redundant, since it's included with GSX.
The one and only reason why you'd want to install the Stand-Alone Addon Manager, is in case you want to updated the modules to the latest version with a smaller download. But with the Live Update, is not really required.
We kept the Stand-Alone Addon Manager available for download only for a single reason: the QW757 *requires* to install the Stand-Alone Addon Manager after it is installed, because its installer hasn't been updated to our latest standard. So, we kept the Stand-Alone Addon manager available for QW757 users that are not interested in any other FSDT product, so they only want to have their airplane running, without installing GSX or an FSDT scenery.