In our climate up here, I would wonder about the durability of the shock typewhen cold and the funtionabillity when -30/-40. I have the the one that Geno's used to sell that is a cable and a tube mounted along the box rail with a spring in it to lighten up the tail gate. doesn't look like they sell it anymore, but I'm onto about 3 years now and no problems yet. They only complaint would be if you touch the cable, you get a nasty black greasy film on you that requires a fair bit of scrubbing to get off. Once you have some sort of gate assist, you end up dropping other peoples tailgates when you open them because you just unlatch it then let go!
I think I will buy the "Plugitright" style next time around since it is totally out of the way and cheap and shouldn't be effected by weather.