There is one little minus in this ... I played a long time ago with rebels and looks like the barbarian rebels cannot recruit any units from their towns .. so they have to wait those brigands ....
Greeks and eastern rebels can recruit some put mostly some light troops .. greek rebels can recruit hoplites who can be the backbone of your army .. so if you want to play with rebels then you should free those greek cities ...
But the biggest downside playng with rebels is that you can not lose any large battles cause you will lose the entire army .. you can not withdraw either