Well I can give some feedback on the Mototrax with my limited experience for what it's worth.
I purchased a 2017 137 new with all the updates done last February and put it on a kx500.
As I say my experience is limited, I have only ridden my set up and a couple camsos on a crf450 and a xc300. As far as my set up I only got in half a dozen rides last year as I work a lot in the winter and I had to do a rebuild on the kx500 when I bought it.
As far as build quality the Mototrax only gave me issues with the tunnel and rear bar rattling off. Design flaw was the bolt's were only threading into one side of the pipe, couple threads maximum. Fix was easy, drill right through the pipe and install longer bolts and nylock nuts. Been issue free since.
Riding wise, my snowbiking experience is limited, but I have ridden and raced dirt bikes my entire life, sledded over 20years, and skied my entire life, I even work as a heli ski guide in the winter, so I have some experience around deep snow.
To me the trail manners of my set up are horrible, worse than the camsos I tried. But once I get in the pow I am blown away at how nimble it is, I can hook hard on a dime, and the track does not feel long at all. It climbs amazingly, imo it will out climb my 02 summit 700 in a straight shot. I also have not been able to get it stuck even with some effort. Last winter wasn't the deepest in BC but I still had it out in 75cm of fresh and I had no problems with trenching. It really seems to plane high in the snow. I know I could have easily got my 700 stuck in the same situation.
My track definitely spins alot and does not want to wheely, but the wheelys could be put down to new rider error....
Loving the kx500, could pull 4th gear huge hill climbs forever last spring.