Curved shaft? Forget it!
Why the dislike of a curved shaft?

The curved shaft is actually more comfortable to use. You can hold the weed eater at a comfortable angle, and the curve 'drops' the cutting edge to ground level without having to stoop. And what's more, you don't have to have all that weight sticking out 6' from your body in order to reach the ground, like you do with a straight shaft. The longer the shaft, the more muscle you use to swing it back and forth. So a curved shaft actually saves you a lot of energy and potential muscle strain by keeping everything closer in to your body for ease of use.

Tough big line is less expensive than the wimpy stuff that everybody uses
I'm with ya on that one! I was surprised that the model I purchased came with two heads. One for the wimpy string and one for the thicker ribbed stuff. I like the option of being able to switch them out. If I'm working around more delicate objects that I might accidentally whap with the line but don't want to damage, I can use the thinner string. But then I can bust out the thicker line (or even the brush cutter blade attachment) for heavier work.

The brush cutter is awesome. It easily takes down 1" diameter and larger stalks that even my riding mower won't tackle. We have a lot of thorny huisache that pops up all over the place, and my riding mower will only lay it over but not cut it. And regular weed eater string (even the heavy stuff) will only whap on the sides of it. But the brush cutter blades saw right through it.