If you are willing to spend the money, then get the 345fr for doing trees. I wanted one but got the fs240 instead. It was about $200 cheaper but you have to buy all the extras seperate. Download the 345 FR manual. It seems that it comes with tri blade, saw blade, trimmer head, limit stop(dedicated saw blade guard), and a really nice harness. The FS240 you have to buy ANY blades, it does not come with a limit stop and it comes with a $20 harness.
Now, the FS240 is lighter and better suited to BRUSHCUTTING. But if you want the power, go 345FR. It does have better antivib and air filtration at the cost of a more complex internals.
I bought the 240 because it was cheaper. Even though I think it could use a little more power, it matches my needs the most closely of anything I found on the market.
Oh, When I looked at Echos big unit, I was unable to find a grass guard that fit it. It was basicaly limited to saw blade only and no harness.