Tbh I wrote my own relay for zapstore: ftsrelay - it does NIP-50 full text search alongside other filters. Bun + sqlite fts, it's working surprisingly well

But I haven't done any serious perf tests.  I would want to have other relays with the same feature set in case something goes wrong with ftsrelay, or for the time when more users would want to run their own zapstore-compatible relays (i.e. they need to be full text indexing certain fields of certain events)

https://github.com/zapstore/ftsrelay