the conclusion:
hobbycity lipos are fine for the MMM as long as you get one with enough of an amp rating for your rig. if you are running a buggy, a 100a constant rating or higher is recommended. if running a truggy or not so heavy MT, 125a or higher is recommended. if running IE, an extended savage flux with 7" tires that weighs 15lbs, 150a or higher is recommended.
all these ratings are for rigs geared for less than 50mph. for over 50mph, but less than 65mph, add 25-50a. for over 65mph, unless you are just doing a few speed runs, all i have to say is good luck
maxamps packs are more likely to cause problems than the zippy and turnigy packs. so, as long as you get a high enough rated battery, you should be fine.
edit: some people may be able to get away with smaller or lower rated packs. it all depends on their driving style. if you are just going to bash, you might not need huge c ratings, but if you are going to drive in tall grass, sand, gravel hills, or race it, you will need better packs.