What can go wrong with a single VM? Billing explosions in the cloud are always to do with auto-scaling services that go wrong. Plus, in that case your alternative is fighting Microsoft, Google or Amazon.
If you run the free tier until the intro period ends you'll know exactly what you can run for free. (There are some free credits during the trial that might skew the resurls) If you do not add anything extra after rhat, there's no visible way you can have a bill larger than 0. But you have to pay attention. Whereas before you would be told "you can't do that", later it'll just go through.