One of the things about a $29/mo RDS instance, though, is that if you're doing full table scans over a million rows, it's going to grind to a crawl and immediately alert you (not explicitly, but via the performance hit) that you're doing something wrong with indexing. Effectively, it's a hard budget cap, and that's super useful for budget-conscious organizations and individuals.
Does PlanetScale have functionality to provide budget alerts? Does it have the ability to speed-throttle calls that would require a budget increase to do effectively without further optimization, which effectively that CPU-capped RDS instance does de facto?
In other words, can I tell PlanetScale to cap my usage and throttle query speed if I exceed row scan limits, rather than blocking me entirely or charging my credit card more? If it doesn't yet have those capabilities, then I think it's fair to say it can easily be worse than an idle RDS host sitting around.