Oh man, you made me laugh with that one... as I was wondering what the heck that was too!
There are some that swear by the gun/cartridge combo as a defense rig, but I would prefer something bigger, fatter, heavier and slower. A co-worker summed it up pretty well I thought - throwing feathers versus bricks.
That said, it is interesting, but I did think of it in terms of what I would use it for - vermin control.
The FN PS90 in full auto mode might change my mind if one or two body guards or SS dudes could empty their 50 round mags on target. But, emptying that 50 round mag can take a heartbeat or 2 and then the mag change is a pita and slow in my opiniion.
TM