Ah, mowing the lawn... always hated doing that, and always will. Mainly because of the weedwhacker. I have personally destroyed four over the years (at my old house) due to having to tap the ground to get more spool out. Apparently, I didn't know my own strength.
At the current house, we have one where the spool comes out on its own... makes it less aggravating. Still a pain in the ass to use, though, because it's battery powered and it never lasts long enough to do the entire yard, despite not having much of a yard to begin with. I end up just doing the front one day, then the back later on. (My wife actually suggested that, since she cares more about the appearance of the front than the back since we don't go there very often.)