I said the exact same thing to the HPI rep on that vid or another official one, and he just gave the same BS line about Castle saying you need 100amps, therefore those lipos are fine.
In reality, I wouldnt run anything less than 5000mah and 25c, regardless of brand, atleast that way you have some kind of overhead.
You'd need someone who knows all the technical lingo & such to argue the point for needing better lipos when using the MMM, otherwise you just get the same repsonses as I see under that video. The HPI reps and tech guys really dont know anything about the MMM system, other than more voltage = faster