The Stihl guy said that I could pretty much use any 8 inch circular saw blade for my FS 110 line trimmer. Any comments or suggestions on best blades.
Use of a blade designed for a circular saw is probably hazardous to your health. Best stick with blades design for trimmers. I recall most costing about $24 bucks and they are very durable. For a bike handle trimmer, I prefer Redmax sst229 blades. Basically a disk with chainsaw teeth cut into it. They sharpen just like 3/8 chain. If you have a loop handle trimmer (with a barrier bar), stick with the stihl 3 point brush knife. Works great and is reversible and very easy to sharpen. Anything the brush knife don’t cut, hit with your chainsaw. As a side note, I don’t think stihl loop handle trimmers come with the mounting hardware for circular blades. I recall purchasing an “optional” kit that includes a much larger trimmer guard. Be careful.
Only use circular blades designed specifically for brushcutters. Any circular blade not specifically designed for a brushcutter is extremely dangerous. I prefer to use a 7" blade that has chainsaw teeth riveted to it. It sharpens with a round chainsaw file. Don't use a blade of larger diameter than what your brushcutter can handle.
Kickback can cause serious injuries. To avoid serious injuries from kickback, mount a circular blade only on a straight-shaft brushcutter equipped with a bicycle handlebar and a blade guard designed specifically for your make and model brushcutter. Never mount a circular blade on a loop-handle trimmer.
The following article provides practical advice on how to use brushcutters with circular blades.
How to choose & use brushcutters - woodlot thinning - includes related information