I used my trekkers for about 75% of my shorter tours last season, and they got the job done. The only major problem I experienced with my trekkers was the, trekker becoming smaller in very cold weather. This of course required immediate attention on the skin track. The problem was easily solved however with a screw driver and some lock-tite later that evening back at home. I'm going to be honest the uphill is a bit like being on stilts compared to other AT set ups, but the reality is, if you're looking at trekkers I doubt you'll be doing long tours on them anyhow, in which case they'll be fine and you will have earn't your downhill that bit more. Trekker don't interface to well with Pivot Series bindings, as they don't engage the brake. Although I've heard of people winding duct tape round the column above the brake to combat this. The high heel piece may be an issue also, as I found the heel piece on the Axial2 series bindings got in the way of the trekker movement, in which case your heel will not return the trekker base, this isn't to be of too much concern as it's just about bearable. (OP nb. I say may be an issue as I'm not sure if the heel piece on the the p18 is high enough or not, from memory the heel piece height isn't an issue)
Sparknotes: Get the job done, don't rely on the original screws staying in there - carry spares and a screwdriver, lock-tite too.
Feel free to PM if you've got anymore questions about Trekkers
Check my blog for updates, reviews and some avi awareness basics: http://aslansskiblog.blogspot.co.uk/
You know you bought the right size if there's more Xs on the label than the door of a porn theatre