durability of plastic soffit intake vent

I'm seeing mostly positive comments about this particular type of soffit intake vent: http://www.everflovent.com/pro_inhaler.html

I'm considering having these installed when I get a new roof. This will be a tear off job with three layers being removed.

Will these plastic moldings become brittle and possibly crack under the weight of snow in the cold weather? Would they crack if when walking around on the roof if you somehow step on the edge of the roof? If they do crack then wouldn't it be a royal pain to replace and reinstall them? Wouldn't any cracks create a direct route for water to enter the interior roof?

Any opinions would be appreciated.

Thank you.