They are not importable because they are not "sporting." Though it is a pump-action, the pistol grip, overall shell capacity and, interestingly enough, marketing materials preclude this as being "suitable or readily adaptable to sporting purposes." I imported a couple of them a few years back, but they were approved and made it through mistakenly and were later forfeited to ATF. If you ever see the photos of the ATF Research Collection, there's one of the Neostead and it's likely one of mine.
The Neostead in theory is a good concept, but as manufactured it's not there. It's very heavy and since weight was already an issue due to the overall design, Truvelo uses a lighter, but more brittle plastic for the stock. The result is a gun that is still too heavy, but also now delicate enough to shatter if dropped from waist height. The mechanism is also very complicated and not very robust and would not withstand any sort of real-world abuse.
The only thing it had going for it is the weight made it shoot very well.
Classic example of a gun that looks and sounds really cool, but has the "oh....." factor when you actually hold one.