So far my usage has been minuscule in comparison to the PS limits. That said, I had been hoping for better tools to identify "problem queries" early instead of just when the billing cycle comes up and so I'm happy to see work in that direction.
Just a random anecdote about PlanetScale:
A few weeks ago I realized their databases did not have the timezone database loaded into them and it wasn't something I could do myself. I needed this so I could do `CONVERT_TZ` to convert from UTC to the user's TZ (for report aggregation). I reached out to support and in about a week they had added it to their roadmap, shipped it, and turned on the new feature for my DBs. They have been a joy to work with so far and I encourage you give them a shot, especially if you are on Aurora Serverless (V1 or V2).