poly is certainly lighter, less wear and tear on the machine to lift it and such. Steel will take hits probably a little better but i havent see a poly broken, or at least anyone ever complain about breaking one on a forum or facebook. not sure what pads are on the bottom of the poly but if it gets worn to the blade back edge somehow, it could probably wear through the poly faster than it would steel. my warn has pads and a steel replaceable edge on it, as im sure they all do.
I have a 60" steel on my honda rancher with the warn full setup, middle mounted with the long tubes. it is nice with the pro pivot for left and right then a winch to lift it. the ability to turn the blade without getting off the machine saves so much time. my driveway is odd shaped and i cant push it all the same direction so it is imperative that i can turn it. warn made it easy back when i bought my setup with a left right toggle switch and a center mounted pivot motor. not sure what they do now but i know they went away from that gear driven single motor. im sure people were destroying gears in them when they hit stuff on the far outer edge of the plow and torqued it.
If i was buying one for my defender, id look at the small boss V, which would be heavier but probably well worth it if you plow a lot of snow.
steve
