I strongly agree - it is nasty to be forced to switch to explorer every time you have a better candidate in the to-check group, especially if you have the source group in a big directory tree.
But I don't like the idea of automatic tag exchange, since source tags tend to be better, at least in a well maintained source (I'd call it target or base) group. The existing tag exchange mechanism is sufficiently easy for me (Ctrl-e + change all + apply).