I have this one, although not a Stihl, it has worked good and I have a couple of extensions that I can get a limb at least 20' high, also the tiller attachment and others work good also. I use it often and have had zero problems.
This is the best limb getter as you can angle the head up and go around the fence rows and kill all the over hanging limbs. I have been doing this for a couple years using Surmount spray and am slowly taking back my fence rows. I have taken out limbs 20' high with this also. Also the Surmount will take out the Cedars and not kill your grass.
http://www.dowagro.com/range/products/surmount.htm
This is the best limb getter as you can angle the head up and go around the fence rows and kill all the over hanging limbs. I have been doing this for a couple years using Surmount spray and am slowly taking back my fence rows. I have taken out limbs 20' high with this also. Also the Surmount will take out the Cedars and not kill your grass.
http://www.dowagro.com/range/products/surmount.htm