As long as there's no military need for them against an invasion there will be zero mines in the ground. No one will hurt themselves with them, unless some storage worker happens to drop a box on their toes.

As of why now, you can't pull out of agreement and start to build up manufacturing and logistics if there's active invasion going on. I hope not a single one of them is ever dug on our Finnish soil, but I'm glad that our military is prepared to use any viable option if they need to.