In my current campaign I allowed the Expert as a PC class amongst the normal PHB ones for people who wanted a high skills class without being a Rogue: one player in paticular wanted to play a non-magical artisan and it was a way to let him be at least slightly viable as a PC.
I didn't notice ahuge balance issue: none of the players were pushing themselves to be optimized, so he stood fine, and when he multiclassed into cleric he remained a distinctive character with valuable skills.
I've not run a game yet using just those three classes, though. I am keen to try it out, though, and it's on my ever-growing list of "Things To GM Eventually"

I've not run a game yet using just those three classes, though. I am keen to try it out, though, and it's on my ever-growing list of "Things To GM Eventually"
