I can't see any features listed that enable me to control costs to prevent surprise bills. If a site got submitted to HN and hugged to not-to-death-because-it-autoscales then I'd wake up to a bunch of alerts and massive outbound bandwidth bill. I don't want that. I want something that stops that happening.
Predictable pricing means that each month my bill is the same: I'm on a $15 plan, I pay $15 a month. No nickel-and-diming, no hidden fees, life is simple. This is a good thing.
Controlling costs means that no matter what happens, my costs will not exceed $x/month. Service might degrade if necessary, but I will not pay for anything above some upper limit.
Seems that DO has the former but not the latter, because if things get out of hand (caused by an attack, a bug in my code, going viral) the customer can be stuck with a bill. Alerts do not alleviate this risk. Pricing that is generally predictable does not alleviate this risk. Only a hard cap does. I want a plan that says "you have 250 GB of traffic, after which requests will fail and you'll get an email". You can make it nicer by sending me a warning email at 200GB so that I have time to upgrade my plan if I want.