Recommend checking out https://github.com/miniflux/v2
n.b. I haven't tested importing 600+ feeds!
I've been self-hosting miniflux [0] for a couple years. Rock solid performance, deployment is easy, upgrades are small but meaningful, and doesn't use anything exotic in the tech stack (mainly Go, some vanilla JS, persists data in PostgreSQL).
I mainly browse on my laptop, but it's pretty decent on mobile.