We hear about free things all the time; in different promotions to all kinds of things, product presentations, samples, demo sessions.
Free actually means that they won’t ask you for any money in return for their products or what else they might offer, but they will still demand something from you. It’s all about the time and attention you are going to offer them. That is what you are going to be paying with.
Even if at first this might not seem like a bad deal, if you consider all the options you have to direct your time and attention to, it might not turn out to be the deal you were hoping for. I am certain you had, at least for a few moments in your life, the feeling that you have wasted your time with something not worth while, that you wasted your time when you could have used it to do something else that mattered, something important, something rewarding, something fun.
Everything has a price, just make sure it is worth it.