Since I teach shotgun, it is inevitable that I get questions about the gun. I bought a Mossberg shockwave to keep handy as a demonstrator to basically do a live show version of what Karl and Ian did in the In-Range video.
That being said, I've been giving it the fairest shake that I can and it's turned out to exceed my admittedly very low expectations. One of the best things you can do to make the Shockwave style gun useful is to mount a Crimson Trace green laser unit to it. The Mossberg comes ready for a rail mount on top and I've got a decent rail screwed on there with the CT module mounted far enough back that I can reach it easily with my right thumb. The stock bead on the gun is useless anyway (on my specimen any bead visible leads to shooting ridiculously high...I suspect it is like that on most of them) so I'm not really giving up anything in terms of sighting.
With the laser mounted on the rail I have a quick, useful sight that allows me to keep the gun at about chest level, which makes it much easier to run the gun rapidly and accurately. Push/pull is much more effective from this position and it doesn't load as much of the felt recoil into your hands as getting the gun up to eye level.
Manipulations with the gun are more awkward because you don't have the stock to assist in support for things like emergency reloads or topping up the tube. Not a problem for those of us with good grip strength, but it would be a huge issue for most people I see in classes. Getting people to properly grip a Glock 19 is tough, much less a chopped down 12 gauge.
I'm toying with the idea of sending mine off to Vang Comp to have them affix Remington rifle style sights to the barrel and putting XS sights for the Remington on it, which I suspect would aid dramatically in the effective use of the gun at eye level should you want to go that route.
Of course, you can "brace" the gun and create a sort of ghetto copy of the SBS as long as you understand that the "brace" will never be as good as a true stock. But it will be more useful than it is in the factory configuration so it's still worth consideration as an upgrade. "Bracing" would be another great application for the rifle-style sights on the barrel, or for buying the Tac-14 and putting the 14" rifle-sighted barrel Suarez sells on it. (As much as I hate to do business with Suarez)
I can't speak for the other names on the list in the original post, but based on what I've discovered to this point I'd say that if you have a high degree of proficiency with a shotgun and you intelligently modify the weapon you can accomplish a hell of a lot with the thing...more than most people would think possible just by looking at it. Like the original Witness Protection gun, it's an expert's weapon. When set up intelligently it can be used very effectively by someone who knows what they are doing, and it gives them the option to have a 12 gauge handy when they otherwise would not. An example would be in a hotel room...I can have a 12 gauge with a light and a laser that fits in my suitcase and nobody is the wiser. (Again...pretty much what the original WP shotgun was intended for) I can use it better than most people can use a properly stocked 12 gauge, but that's a tad like being the skinniest girl at fat camp.
It's absolutely no match for a shotgun with a proper stock on it. Anyone who can use a Shockwave style shotgun can use a properly stocked gun better in any objective measure...but if they can't have a stocked shotgun then the Shockwave style weapon gives them most of what they would get from the properly stocked shotgun in a package they have ready access to.
The problem, at least as I see it, is that these things are being bought as someone's first shotgun. As in they have no real shotgun experience and then they buy one of these things because they want a home defense shotgun...and that is a recipe for disaster. They are heavy, awkward to handle, and they recoil like a motherfucker if you don't know what you are doing. The number of people who are not already proficient with a shotgun that will be willing to invest the time and effort learning to become proficient with the thing is going to be infinitesimally small.
It absolutely doesn't do anything better than a properly stocked shotgun except go places where you can't have a properly stocked shotgun. That is its sole practical virtue, IMO.