Yes, I made a bunch of these last summer and they are sharp, but I folded them on the edges so they would not be sharp. I also punched my holes with an actual hole punch.
I think it would be great to make a double batch of these and not only mark the outside of your plant, but bury one under the plant, so when vermin run off with your tag, you can at least ID it later when it is time to harvest/divide.