We have both. Mother-in-law got the mini saw for Christmas a few years ago, we bought the big one for removing 5-10 fallen locusts. 1) Locust trees are a bitch to cut with a handsaw or axe, and 2) the 16" saw does surprisingly well. The big battery is mandatory, though. I think I have a couple of the medium sized ones, and they were good for 4 cuts each. The big one had ~25% left after chopping up 40 feet of tree. Also, buy a "supercharger", cause that giganto battery takes 6-7(?) hours to charge on the little one.
Small one deffo punches above it's weight, and you can buy chains at pretty much any hardware store.