Not sure Stihl do a 4-stroke. I've used Stihl, Husqvarna, and Honda professional strimmers/brush cutters (and I think I'm right in saying that a brush cutter just has the straight shaft and they'll all take a strimmer head, and you won't get a professional quality strimmer as such). I'd rate the honda 4-stroke above the others, it's a lot more ecconomical on fuel, and quieter too in my view. They all have decent enough auto-feed strimmer heads, but you might have to experiment a bit to find the best stimmer cord - fine grass, rough grass, nettles, thistles, and brambles can all take a different cord for best results. I'm not up on the models, but but I guess you're looking at a machine in the £400-500 bracket.