I use the Stihl KM 100 R with a couple of attachments and I'm quite pleased with it.
With the standard metal brush-cutter head FS-KM, forget the metal blade that comes with it and buy the plastic bolt on head that has 3x disposable plastic tab blades, I found that more effective. (The combi handle is possibly less effective than a conventional 'cow-horn' handled strimmer, but the cow-horn handles would make a chainsaw or hedge-trimmer configuration difficult to use).
Near trees I use the FH-KM head along the ground - like a shortened hedge-trimmer, but with an added stainless steel shoe to reduce wear to the housing. (It'll still perform as an angle adjustable hedgetrimmer, but the reciprocating cutter bar is shorter).
The chainsaw head with an extension pole is quite effective (possibly less fatigue on a long work-scope with a chest harness). I've used it extensively on neglected tall hawthorn hedges and low overhanging ash tree branches.
I managed to get a rotavator head on a very good deal (Stihl prices seem quite consistent across most suppliers). It's only really for lightweight use, but I have lots of compost to turn over and stuff to work into the top of light soil, seems to perform adequately for that.
There are suggestions on some power tool and review forums that some other manufacturer tool-heads and devices may be interchangeable.
Why did I get it?
Probably compactness (can be kept out of sight in the back of the Landrover) compared to a full-size strimmer + small chainsaw + small hedge-trimmer, reasonable price compared to individual tools and historically finding Stihl products reliable with decent options for service and spares.