Planetscale is definitely popular and they get a lot of free advertisement from tech influencers (may change without the free tier) but most people I know in enterprise haven't heard of it.
For those that don’t have experience running companies with permissive free tiers, free tiers often act as a honeypot for a certain category of users that (1) don’t and will never pay for your product, (2) complain loudly and often and (3) eat up your support time.
This category of user is equally toxic to any competitor’s platform. The best B2B companies paywall early and set the bar high.