Wow, surprising to me how many guys have axes. They are an important tool to me as I heat with wood. All of mine are probably at least seventy years old, all are what I consider to be family heirlooms (except the handle-less one I found in the middle of the road recently).
I grew up using axes and the first time I needed a new handle I was shocked to learn the awful truth-- curved handles and double-bit axes are no longer done and I still am not sure if that was a family thing or something that fell from favor but ever double bit axe I have or have used has a curved handle. It make so much sense: one side is for roots or anything else that might tend to dull the edge-- a piece of barbed wire grown into a log or what have you. You can easily tell by the feel of the handle which edge you're using and actually switch to one or the other on the back swing. So, the one edge is kept max sharp for best cutting.
When I broke a handle a few years ago it was such a surprise to find they don't make these and then I did remember Dad re-handling one maybe 15 years ago and he had to modify the curved handle to fit the eye of a double bit axe. Anyway it is a most worthwhile axe format. I have a few single-bit axes but seldom use them. The hammer side is not something I ever need but a second edge is something I often need.