Haven't tried the Nu-Teck, but I have something that's very similar in design and material: http://www.greentyre.co.uk/26inch.html
I've even gone to the effort of making one into a winter tire by putting studs in it, as fixing a flat along the side of the road in freezing temperatures can be outright nasty.

And the verdict is:
- mounting was a pain. I'm so glad that the enclosed mounting spatula didn't break. If it had, I'd still be picking plastic shrapnel out of my body. Eventually I resorted to using a carpenter's bench as a rack to stretch the tire on to the rim.
Knowing how hard it was to get them on, I have no fears of the tire coming off unintentionally. If you read up on the stuff you'll find the manufacturer's stressing the importance of having the correct fit between the tire and the rim.
This is your first concern - first figure out which tires that'll be a good fit to your rim, then look for which tread patterns, PSI equivalents and widths that are available.
I got about 200 miles on them before switching to my summer wheels, and they stayed solidly in place for that duration.
- Mine have that elevated ridge in the center, so the pattern isn't that good for braking on hardpack. Next season I'll cut some notches into it.
- cornering on hardpack/ice is pretty much as I expect from the number of studs I'm using.
- on wet tarmac they're nothing special either way. No surprises.
- grip characteristics seemed to change once the surface from the mold had worn away.
- on cobblestones and when crossing thickly painted lane markers they're definitely more squirrely than any regular tire I've ever ridden. Still entirely manageable though.
- dry tarmac is entirely uneventful
- If there is a difference in rolling resistance, it is smaller than all the other differences that influence my regular rides. But then I'm using what's supposedly a custom, 65 PSI equivalent. YMMV.
-on smooth roads I have no issues with these, but they do ride very harsh on uneven ground. Passing a curb, even with the best of intentions deliver a bone-jarring impact.
My rims were OK, but I can certainly see the potential for trouble there. But then I'm using what's supposedly a custom, 65 PSI equivalent. YMMV.
- biggest objection I have is the ride quality and the temperature dependency. For the weather range where I most wanted to use this tire it's like riding directly on the rim, quite bad actually. But when days turned warmer the ride was/is OK.
- I will admit to being worried by thoughts of wheel survival. Impacts are harsh. But 200 miles kinda hints that it might not be as bad as I think.
- had a good look at them when I switched to summer gear, and they seem to be wearing rather rapidly. Can't tell yet it it's just more of the mold features breaking away, or if I'm beginning to lose functional amounts of material already.

In all I'll say judgment is still pending. Mine are supposedly extra hard, so they ride extra harsh. Had the result gotten closer to the stated PSI equivalent in the temperature range where I most wanted to use them I'd probably have been more pleased.
It is nice though, being able to coast right through patches of broken glass in blissful unconcern.

They should probably be seen as a niche product. They're different, and there is a trade-off. For some it will be worth it while others won't like it. But if you're troubled by flats and have the money to spare it's kinda silly not to try them.