I prefer using regular grunts instead of the M grunts because they don't have radio or artillery support but if u want to use M grunts then use it no ones stopping you but still if u want M grunts you will need recon tank for artillery support Bonus tip: Mobile howitzer is a good support unit good range can move without getting towed good hp and good dmg on vehicles but it does have cooldown for every shot
I have a tips for rigged or some campaign that usefull sometime use enemy morale for your avantage you can get a infantry and down the morale of a enemy unit and after get enemy unit that can really help you and in some situation that can be better than detroy the unit even if the captured unit have low hp
