I'm also in favor of a longer length, since I like to use it for walking. Once you get on the slopes at all, I put when trekking poles away, and go to the axe. I use an old Cassin Ghost 70cm, and I wouldn't think the weight difference between 50 and 70cm (for these types of lightweight axes) would be almost anything. I don't want to stoop over to hit the ground with it, and I'm not usually on such steep slopes that the length is a problem.
As everyone else has said, if you get one, learn how to use one and PRACTICE. As I was told when I took a winter mountaineering course, if you have to self-arrest, you have already failed. The key is to never ever get to that point, via climbing in balance, self-belay if necessary, etc. You start sliding and you are in trouble, up to and including death (depending on the run-out).
FYI, I sold my Camp aluminum crampons, and plan to only use microspikes in the future in the high Sierra. Even when I have done multi-week trips in the snow, I only ever used them first thing in the morning (when the snow was icy).