I've had an FS130 for 8 years. The 4 mix takes a little getting used to, but mainly how it sounds due to the way it conserves power. I guess it's a sort of governor, but even medium weeds and brush can't slow it. So when at full throttle (which is what it's supposed to be run all the time) it will sound like it's under powered but that's because the governor is holding it back not that it is slowing due to the work at hand. It's still muscling through everything you throw at it. Get it into heavier brush or weeds and it sounds better in my opinion. That's when it sounds like it's running wide open and is still keeping up with the heavy stuff.
I always run Stihl oil, either semi or full synthetic. I have never run it dry to store, at least not on purpose, and it always starts right up after hanging there for months. If buying another trimmer, I would stick with Stihl. I think either brand would be fine, and the better dealer support might swing your decision.