Yes, don't hit people with a steel mace. Particularly not if you're trying to have a friendly game.
As for how durable, the head is just fine. The haft, I'm not sure. It would hold up for a while, I'm sure, but I don't know that it's a particularly good hardwood. But even in period, hafts would fail and get replaced. Nothing made of wood is going to last forever, especially if it's being struck and torqued.
It should be great against melons. But something to be careful with (and this is true of any test-cutting), is check your surroundings, and angle your swings so that WHEN (not "if") your target goes flying, it won't hit anything important, such as a bystander. Maces tend to fling melons around, because the melon doesn't weigh enough to resist the hit. Downward strikes are your friend here, and of course that means you need to have a stand for the melons that you don't mind getting bashed up with maces.