If you have Milwaukee tools and batteries, buy a Milwaukee string trimmer. I've had a Pro Husky 225R and a Stihl Kombi.
I have 7 acres, including a 1 acre yard. I wish they made the Milwaukee years ago and saved me all the years of hassle. I'm a power tool guy and love things with engines, but a gas string trimmer is a hassle and frustration I can do without. I was incredibly surprised at how well the Milwaukee trimmer works. It's lightweight, quiet, powerful and holds a ton of string. And it starts every time I depress the little trigger. I have a couple of the larger amp hour batteries and one battery will do my whole 1 acre yard.