Thanks for some great software!
I agree with the request to facilitate easy direct visual comparison between fonts.
I do not like the workaround that requires tagging. It should be an immediate feature that, as a user selects fonts in the fonts list, a comparison can be seen.
My favorite implementation of font comparisons so far can be seen in Linotype FontExplorer X. As the user selects fonts in the font list, a comparison pane simply appends the rendering in realtime, no tag selection required:
I note this feature has been requested in: