I use my FS90R all the time...

String head for grass

Tri blade for things like greenbriars etc etc

Quad/Square for larger items like willows.

Circular saw blade for 2” up stalks.

I dunno if the machine your looking at has the same CC’s or not, but if I recall the FS90R was the smaller of the machines stihl says should “safely” operate the blades... it sounds like a harley weed whacker lol, but its not near as strong as my buddys stihl that has the handle bars.... but I use it for grass around the house more often than not and didnt want a lincoln town car for a weed whacker.