I'd admire it a lot more if it were actually useful. A small shotgun has it's place. A KSG is the same length and worlds more useful.
Define "useful". So, Mossberg separated me from my money. I like the idea and size. Sawed off/PGO shotguns have been around for close to two hundred years...so this isn't anything new, just legally easier to obtain. Now, as to potential, usefulness, after spending a few shooting sessions with it, I would now put it in the useful-niche category. I was really shocked at the range this can be effective at. I was getting pie-plate patterns (OO buck) out to 30 yards which was impressive. As to "aiming", it's much easier with this bird-head grip, but still takes considerable practice. As good as it seemed to pattern, my son found out how easy it is to miss an entire silhouette target from about 5 yards. It's not bad from the hip, but actually aimed, it is consistently accurate. I'm going to try it out with O Buck, 1-Buck and 4-Buck.
Is it useful? For a compact, short-range (inside 25 yards), I would say it's useful. The big "but" is that it takes some practice (about 50 rounds of birdshot) to really figure out the aiming to be consistent. Will this replace my regular 590 by the bed? Nope. Could it? Sure. It does (IMHO) need a light on the fore-end to be a true HD weapon. A laser is intriguing since the majority of shooting is more pointing than conventional aiming.
At the end of the day, it's a gun, it shoots. It's larger than a handgun with less capacity (except subcompacts and revolvers), and it's not as effective past 25-30 yards than a conventional shotgun. It's' a niche gun that would be a serviceable defensive tool from a vehicle or tight quarters; it could be a handy breaching tool with the right rounds in a more compact package than a regular shotgun and avoiding the NFA circus. So it can be useful and it does have potential (I would really rather, and plan, to have an SBS), but like any defensive firearm, it's going to take (likely more) practice. If it doesn't appeal to you or tickle your fancy, then I can see the questions about useful or potential. That's not a knock, it's simply a firearm that isn't for everybody and it's definitely a niche purpose.