Do the straight ones work better for taller people? I find that I'm constantly bending my back while using mine.
yes - without a doubt. I did 4 yrs of trimming for Ames P&R where we had straight shaft trimmers. Then inexplicably (not paying attention) I bought a curved shaft craftsman trimmer. It worked fine - but same problem as you and I'm 6'3".
A few on the market (electric) have adjustable length. I know the B&D one I just got did. Noticed a couple others did as well.