Ok, I didn't see the runtime numbers before. Sounds like I was a bit too optimistic (it did sound a little too good to be true).
15 minutes doesn't sound too good, but that's for how much time the string is spinning. Electric machines don't need to idle. Four AP160 batteries should give you 2 hours of run time. Do you really think it would be possible to drain four of them in one day?
Based on that (and the higher battery cost), the breakeven would be more like 21 months. That's still well under half the battery's lifetime.
Oh, and it looks like the cordless chainsaw is indeed brushless. I can't confirm if any of their other cordless tools are, but brushless motors are pretty tolerant of being run wet.
So the question is, would a pro actually get the full 30 minutes of working time on each battery?