Southtree

Your lawn looks immaculate. Might be the herbicide, 'Weed n Feed' etc you use. Pretty common for landscapers, lawn guys etc to get tunnel vision when reading the warning label on that stuff. If you are serious about retaining the tree, I would encourage you to get a local ISA Certified Arborist to take a look - pretty hard to tell from photos

Yeah, good plan. I have the electric start one and the only issue I've ever had with the trimmer was the bolt for the electric start rattling loose. The electric start model actually has a pull cord too though and I tend to just use that. She doesn't like excessively bumpy ground but you will be able to manhandle her over most stuff and she won't pull you up really steep hills but you shouldn't have to push too hard. I've had mine for 3 odd years, give her constant abuse, and she hasn't missed a beat yet. If she died tomorrow, I would be straight out to get another one.

I couldn't recommend the DR Trimmer highly enough. I have a self propelled unit and use it all the time around home in NZ. I am currently in the process of clearing around 3 acres of overgrown paddocks of neck high grass, gorse, and broom and replanting in native trees When using the correct cord you should have minimal breakages. But if you throw on the circular saw blade it will destroy anything. Very good for clearing unwanted self seeded tree's, gorse etc - no bending over, no sore back! If you are going to buy one, I'd definitely go for the self propelled unit though - makes operating on hills so much easier