"He doesn't seem to be evil... But more importantly: Is he strong?" Fairy Tail is still faithfully following the first master's philosophy.

It really shouldn't be much of a problem to ponder if two Fairy Tail teams can truly fight each other by giving their all. In fact they might fight each other even more gleefully than strangers. The only obvious problem here would be Gray and Juvia. Elfman and Mirajane as well, but on the other hand Elfman is not the real member of the A team.