I have the 350BT plainedge and though I do not consider it a really hard-use knife, it's a lot more solid than it appears at first. The whole outer shell is Zytel, but is reinforced with stainless steel liners.
It's not my everyday main carry, so I can't comment yet on liner wear; however, as the blade at pivot point is nearly flush with the liners, if the liner works itself all the way over, it won't 'stick' and become a fixed blade. The liner on mine snaps all the way over anyway and is rock-solid.
I consider it mostly as a nicely-done, low-key gentleman's knife.