With Linode, if you sign up for a month and then cancel after a day, you get a prorated Linode credit. If you spin up five basic Linodes and delete them all after a day, you get nearly $100 back in Linode credit but you still get charged for $100. With DO, you get charged for only what you use. If you spin up a droplet and then delete it after a day, you only get charged for like $0.17. To my broke college student self, anyway, that's a preferable business model.
Digital Ocean bills hourly assuming 28-day months (so, [price per month / 672] per hour) and caps at the monthly rate. There's no circumstance under which you're paying more than the advertised monthly rate. You just get 2-3 "free" days in most months.
Nope, they don't. They keep a running total of how much server you've "used" (like, I've currently used $2.95 for the last few days of several droplets) and bill you at the end of the month.
Not only that, but they recently just canceled out my outstanding balance of $0.85 when I asked if it was possible to only pay them what I owed, instead of a full $5. That wasn't even surprising, considering the way they've been operating.