Let them do it and lose all the revenue from those players. Spoofers etc probably put more money into the game than casual players.
They posted this a little while back and another article stating they're trying to put bans in place.
I've been using one every day since March with no issues whatsoever, I've also seen nothing, anywhere to suggest anyone will get banned for using one.
And what? Trying to be funny but clearly not
Wristband is 100 times better as it can autospin stops and catch Pokémon - However you will go through Pokéballs like they are pennies lol. Also you can charge the wristband.