Each block holds four projectiles. That means you would need to change blocks at a rate 7.5 times faster than a conventional 30 round mag. Not very advantageous in a firefight.
That’s assuming one wants to use the “top speed” cited, and not the more normal operating modes.
Think of it (I am assuming) as a sort of burst-fire feature. One press of the trigger shoots four, then the magazine feeds another block of four. Press the trigger again, etc.