Looks interesting but I can't see any details like max coal

These guys prices are off the wall. 

While they do look awesome, they also look like they're a slap in ready extended factory magazine. While that may be enough for a lot of people, for me, I'd hold out and spend the money on a CDI bottom metal and use AICS metal mags with more COAL. If I'm upgrading, I want more function that just number of rounds.