Normally i don't use client rulers but during a terrible war with Macadonia (as Romanii) i had to use the last of my reserves cuz Maca had like toooooo many fullstacks. Mind you i didnt start the war, but took a border town from the Getai. Maca was even my ally!!!!

But i started winning and had to little time to establish gov II's and had not enough FM's so i started building gov IV's. Now the whole of Greece is ruled by client rulers. So if needed i use them extensivly.

Merc. Generals i use as fireman to plug holes in my limes. If the need is there my two Merc. Generals are there to try to fix a border dispute or slow down the enemy till the legion or consular army (if needed) can take over the war or battle.

My two cents.....