there is a thread on NPW's just "round the corner".
I have some experience with ATB's and NPW's, but none on the snow yet.
To your question:
""What winds can you use these kites in with a mountainboard and snowboard?""
As there are several sizes, you can cover the whole windrange. I found a NPW5 250 (4.8 m2) to deliver enough pull in winds of about 8/12 mph (I weight 84 kg). Upper limit depends very much on your skills.
For snowkiting (say 3 to 4 Bft.)you might want more pull, but it will also depend on the kind of snow you have (packed, powder etc.) and, of course, on your weight.
""Are they easy to launch?""
With 4-lines yes, definitely. With 2 lines it takes a little practice.
""Do they have a brake?""
If you fly them 4-line, yes. It works like in normal quad kites. In 2 line modus, no.
""Can you fly them with a classic 4 line kitesurfing bar?""
If you mean "in 4-line modus with a bar", not that I know. You can surely fly them as 2-line with a bar, or even with the 4 lines attached, but you wouldn't be able to operate the brakes independently, wich means losing most (or all?)of the brake function.
Somebody might have better ideas concerning this aspect.
In general, I find handles better for land use, especially in combination with quads.
"DO they boost any air?? Like inflatables?"
NPW5 are not recommended for jumping. They do not have a very big lift, and they are not very stable. Anyway, you can get huge airs with many ram airs as well.
""Finally what line length is recommended?""
As far as I know 25m to 30m should be standard.
Here a few comments on NPW5 I already posted in the pther thread:
The pull of the NPW5 is impressive, but definitely NOT smooth.
Upwind performance is not to compare with that of a good ram air.
They are very cheap, although kites like the Firebees are not much more expensive.
They are indestructable.
They take very little room, so you could always have a full set in your car.
They look funky!
All in all, I would recommend it to anybody who wants to start with quad-kite-traction. I don't think it is a choice for those who look for real performance.
If the new NPW9 really has 10/15% more upwind capabilities, it would become more interesting.