I've been using my Sawzall with a pruning blade for the last several years on medium sized tree branches. It is actually works quite well. The pruning blades are about 9-10 inches, so a branch up to 18 inches is not a problem.
Did you see the first posts?
That said, a Sawzall with a pruning blade is a damned
light saber on anything it's long enough to cut. I love that setup, and it's big enough for most things most people will have to cut.
Add to that the battery power if you're going cordless, the relatively small, lightweight package, decent ergonomics, and you're going to have an easy time of things.
I don't touch a chainsaw unless that thing just plain isn't long enough to do something.