It doesn't mean because it's free, you're going to get banned. It all depends on what you're going to bot, which script you're going to use, how long you're going to bot for. Mirror client is available to VIP which will supposedly decrease the chance of getting a ban as Jagex can't detect that you're using a different client to access their game. I've been using it for a couple of days now and I haven't been banned yet, in the end the decision is up to you.