Since the August bundle includes two games from my wishlist ("Call of Cthulhu" and "Vampyr") I'm tempted but just to be sure if I understand the concept correctly: I can buy the August bundle for this price and then cancel Choice before the next payment so I only have to pay one month, right?
You can cancel or pause. If you pause, Humble automatically unpauses your subscription with the new bundle release each month and you have to actively pause again or they will charge you shortly before the bundle ends. So if you're only interested in a one-time purchase and don't want to check the bundle each month, cancel might be the better option for you.
I think the choice between pausing or canceling only makes a difference for Classic plan subscribers (those who were already subscribed to Humble Monthly at the time of the switch to Humble Choice, you can't opt into it anymore if you weren't). Because if you cancel as a Classic plan subscriber, you lose all access to the Classic plan and can't ever get back to it. So they kind of hold the old subscribers hostage with this (in exchange for a lower price and larger package), but for new subscibers it doesn't really matter.
Although, as a Classic subscriber, every time I paused the subscription lately, they offered to lower the price for the current bundle if I reconsidered. Not sure if they do that on other plans, too. If so, that could be an incentive to pause instead of cancelling as well. That being said, it's never caused me to reconsider so far. It just seems very desperate on their part,