Does it have to be Stihl? I really used to be a Stihl Fanboy until I got a Maruyama trimmer. Also, is it mainly going to be used for trimming grass or brush cutting? A bike handled trimmer can't be used as an edger and it's overall much slower to use to trim around driveways, fences and the house. But if you're going to be using as a brush cutter then the bike handles would lend itself to be better.
I have bad arthritis now and I use a shoulder strap and a Darwin's grip. It really makes using a trimmer much much easier.
If you just have to have a Stihl, I recommend staying away from a 4-Mix engine such as a FS131.
Fast forward to around to 40 seconds.