I look forward to reading any advice...
I have an older Craftsman weedwacker and I always dread running out of string. You have to feed in 100' of it counter clockwise and if binds up, you have start over. Even when it was brand new, it never really worked right (bumping for more string) and I always find myself pulling it out manually. Plus, I go through a lot of string with chain link fences.
I typically do a lot of cursing when I use it.