Dolmar were the first to introduce a petrol powered chainsaw back in 1927.
They make not bad product but why go to a 4 stroke trimmer? (now for a debate)
4 strokes give good torque at low end but 2 strokes make the head spin quicker on take up.
With a strimmer all you are looking to do is make the head spin as fast as possible with the least amount of drag.