Sad to hear what you are going through, I personally know a little about that -- a few years ago I was merely reaching between the bucket seats in my car to get something that was not overly heavy from the rear, and messed up my rotor cuff (or is it cup?) and was that ever painful!! I feel your pain! Luckily I didn't tear mine, but it still took what seemed like forever to heal, and I had to be so careful during that time.
Well, the weedeater (or weedwacker as some people call them) I prefer to use on trimming around retaining walls and sidewalks (lightweight work) is my heavier electric (battery operated) weedeater. For the areas with taller, tougher weeds like around the wooded areas, we have the gas, but personally, I don't enjoy having to pull, and pull, and pull to get it started (not always as hard as that to start, but when it is, it's a real pain!).
A short story on pulling and pulling here -- many years ago we had an old push mower, old before we received it, and I just hated using that thing as it was always difficult to start. Finally, one day after pulling, pulling, and pulling, trying desperately to start it, I had just had it with it and visualized walking over to our ravine and just tossing it over! Up to that point DH didn't want me to go buy a new one. The next day, I drove to Anderson's in Columbus and purchased a new, Lawn Boy push mower without talking to DH about it! I thought since I was the one doing all of the mowing, I was going to make it easier on myself, plus I'm the one who paid for it.