Here on our farm we use a Stihl Brush cutter. For us, we compared the cost of this cutter against the cost of hiring a worker. Although by comparison, the cost of labor is inexpensive in Brazil, with a worker costing around R$80 a day. That's about $27 (US).
Farm and garden machinery are expensive here and it wasn't a decision we took lightly. In the end we did buy a brush cutter and have had the same one for 8 years.
We have the FS85 which is classed as a landowner series. They also do a professional range.
Read more about our experience with our Stihl cutter.
When I look back at what we spent on wages for workers here, I feel this was money wasted. Although the two of us can't do the same amount of work as a local, what money we make, is ours.
Therefore my advice to anyone thinking of buying a brush cutter would be, do it. If you are physically able to use the machine, buy it because the money you save in not paying wages will more than pay for the machine.
We see the machinery we buy as an investment, not as an expenditure. Of course there are ongoing costs such as gasoline (petrol), oil, and then parts. The repairs my husband will normally do himself with guidance from watching YouTube videos. There are a bank of helpful videos about problem solving and how to replace parts.
My husband cuts through most types of grasses and weeds using the nylon line. Although we have a blade attachment, this is rarely used except on small shrubs.