Brian.......you know the saying - It sounds too good to be true? I just checked this website out - sounds like an elastomeric to me - just judging by the film thicknesses and such.
50 years is a long time - I doubt you would ever get your use out of it - are you going to keep your house that long? How many times could you paint it with high quality paint during the time you own it for the price of this stuff?
What about recoat? What if you don't like the color in 10 years?
I also wonder about it being 600% elastic - yet mildew resistant. Elastomeric coatings (coatings that are more than 100% elastic) are very soft - they have to be to stretch like that - mildew very badly - can't be helped - the mildew sticks to the soft surface.
Lots of questions.........after 18 years in the paint business......sounds strange to me.
Stick with a good quality 100% Acrylic latex paint properly applied - over a properly prepped surface...........