I first bought the FS70 with the easy start system. Tried it for a week, didn't like it, returned it and bought the 100. It was about $30 more, but well worth the money. Its very light, powerful and easy to start. The only thing that is lacking with the 100 is that it is a dedicated line trimmer, and cannot be used for any other implements. The 110 is the best of both worlds. It is powerful and the head can be changed to use with any of the other implements, but its a heavier unit.
I didn't like the so called "easy start" system, on the FS70. It may start in one pull rather then two, but it requires A LOT more pulling force, which I didn't like. If mine had a loop on the pull line, instead of a "T", you would be able to start it with your pinky. Its that easy to pull.
In my opinion the professional series is the way to go. My Dad bought one 27 yrs ago and is still using it today. That pretty much says it all.