Basically, for the same price HBO Now was, you are getting a replacement for it with HBO Max. And for now, you can get it for free with an AT&T unlimited mobile plan or an AT&T fiber gigabit plan. So if you have either of those, you are good to go. But be sure to first log into your AT&T account and activate the promotion.
If you own a Roku or Fire TV, you still can't watch HBO Max until they come to some kind of agreement. It works great on Apple TV, and Nvidia SHIELD though. And you can still cast your screen from a phone or computer to watch it on your TV with Roku.
But you will need to use Roku casting. Check Out - How to cast to your TV Screen with Roku for more information on how to get HBO Max working on your Roku.