Given that you own the smaller PE, that's good. I'm sure you'll need your backup notebook when it comes time for proving trig identities - that's when I always had my students turn their papers landscape.

When I tutored, I was using one of the early Acer Travelmate tablet PCs. I would have found it awkward to let my students write on something smaller (I can deal with a smaller surface, but when the kids are figuring things out, the added real estate is helpful). Do you use your PE just for your writing, or do you let you students write on it, too?