Michael, my experience with Stihl goes back to 1982, when the first 2-stroke landscaping machine I operated was a Stihl backpack brushcutter. I've owned 12 Stihl machines and currently have 9, the oldest at present being 16 yrs old.
Experience tells me carbs used by Stihl on their machines in the last ten years are not generally as good as the ones they used to fit twenty plus years ago. I could be wrong but I seem to remember Stihl bought out Zama some time ago and it was around then that carb quality started to decline.
I've done numerous carb strip-downs over the years, mostly just for routine maintenance but sometimes to cure uncharacteristic lumpiness.
The worst carb experience has been on a KM55R bought ten years ago. Thorough ultrasonicking, new diaphragms, gaskets, even new metering needle and spring didn't help. It's currently on its third carb, the last two being non-OEM ones bought direct from China for under £7, after my local Stihl dealer wanted £125 & VAT about five years ago just to supply an OEM replacement for the first one that went phut.
One thing it's nearly always necessary to do, in my experience, as soon as your machine is run in if not before, is to adjust the high and low mixture screws to optimize throttle response from idle and not to have the engine running too lean at the top end.
My best Stihl strimmer has probably been my KM130R Kombi, which has the 4-mix engine. Have had it thirteen years and only had to reset the valves twice. It has a solid steel driveshaft (unlike some of the other Stihl strimmers/Kombis) and more grunt than a herd of pigs. It's too powerful for tickling round trees and routine lawncare. My preferred line-cutting head is the Autocut 25-2.
As others have said, a hedgetrimmer is good on thick brambles. My KM130R will cut through all but the very thickest brambles with just the line head, but the downside is you end up having to bump out more line much too frequently. The Stihl KM-HL hedgetrimmer attachment for Kombi engines lets you cut brambles effortlessly without excessive bending down.