I almost coughed up a lung last time I was exposed to the deadly fumes of Moisture Cured Polyurethane. This was really mean stuff. Back then this stuff contained up to 7% toluene, this is the stuff that glue sniffers die on. But it appears at least some companies have reduced the amount of this deadly toxin. Gerners has reduced it to 1% and that is much better. It will still affect the floor guys, and will be gassing off for up to 30 days after.
And the bad new is this has about 50% Xylene, which is a skin irritant, but is also highly flammable. Read about similar flammables in the lacquer article in the Floored News. Frankly I wouldn't touch this stuff.
Yes, it is very hard and very clear (at first), but all the jobs we did got scratched up anyway. After 5 years it does amber quite a bit. And because it has to be applied by a pro, it is a impractical finish for home use. You cannot do touch up or re-coats yourself with this stuff. I speak from experience, we used to do commercial jobs with MCU all the time. But we switched to Street Shoe because of it lower toxicity, for us and the owner.
As always your Most humble servant, Joseph, the Wood Floor Doctor.