I know, was tongue in cheek here too!
I like how they started off doing pushbikes and sewing machines and stuff and then just went "fuck it, let's make guns again!"
According to MCM's own website airsoft guns are banned from all their events so...
https://www.mcmcomiccon.com/london/en-us/costume-weapons-props-rules.html
Maybe the local security haven't been kept in the loop.
I currently have four guns I've never skirmished (yet) and loads more bits and knick knacks that I've bought because they seemed like a good idea, tried once or twice and then consigned to the drawer of doom (final resting place of three different flip to side magnifiers for example).
Where are you finding decent LiFe stick packs? They were all the rage for airsoft a few years back but most places only seem to have one or two choices these days (or are you repurposing RC packs?)
My go-to? A Platatac Peacekeeper MK1.
Can carry 6 7.62 mags or 9 5.56 ones plus pyro, water, the whole 9 yards. Not cheap though.
Also - you haven't told us what you use, what sort of games you play etc.
Unfortunately most airsofters wouldn't know a Newton-metre if it stole all their apples.
While motors don't work in C they do respond differently when the supply current is governing their performance; if a battery can't supply enough current quickly enough then performance will suffer in an AEG because that initial spin up is where the motor will spend a lot of its time. It's less relevant in things like drones or RC planes because once you get the rotor spinning and you've overcome that moment of inertia then the motor can settle into a fairly consistent running current. Once you reach that "steady" state then the capacity calculations etc make more sense because your load behaves more like the graphs that battery manufacturers like to throw around. Even when you run an AEG in constant full auto, the load is never stable. Every cycle the gears have to compress the spring and then it releases so the load comes off the motor. The current draw is never smooth and the battery's ability to deliver a lot of current quickly becomes more important than the mAh rating as long as it is sufficiently high.
Undoubtedly, though I do question their marketing spiel that a low C, high capacity battery is equivalent to a smaller high C battery in this application.