I have a Stihl FS-90R, which I love, lots of power and reasonable on the weight, and I've never had a problem with it.
Never had a Shindaiwa other than an EB-212 handheld blower, which never really ran right, even out of the box.
The ECHOs are a different story, got an SRM-2601 (1999, 25.4 cc) and an SRM-3100 (1997, 30.5 cc), neither have really had much other than an air filter, fuel filter, and spark plug here and there. Of course, those are the old Echos, I honestly don't have much input for their newer trimmers/Multi-tool system. What I can tell you is that my Echo PB-250 runs way too lean, but there aren't any freakin' carburetor adjustments!