So I was pondering about beacons after me and Quiet got one. And I was thinking of setting up a beacon at a mob spawner however that would be classified as an advantage, I was wondering if it could be clarified whether they were illegal or not considering the trouble to get the beacons.
I would recommend the roof of the nether if you're sure that you have strong enough gear to kill it without being killed. That way there's nothing to blow up or fall into.