It's a shame that Google haven't managed to come up with a scale to zero option or serverless alternative that's compatible.
But what would scare me the most, is that google can easily shut this thing down.
Using Google spreadsheets as a backend will just cause them to charge everyone later.
Sheet Ninja isn't free. Even on their side, "free" does not mean what you think it means.
Unless things have improved it's also hideously slow, like trivial queries on a small table taking tens of milliseconds. Though I guess that if the alternative is google sheets that's not really a concern.