I searched here for poly tracks, and found zip. WTH? Figgered they would have been discussed a lot. I saw a video of a machine using them, and they looked like they worked real well. What do you folks know about them, and what brand might I have seen so I can do more research. Durable? Spendy? etc. Google gave me little; maybe "poly tracks" is not the right wording??? Thanks. j