I assume they mean startup speed (cold-start). Since they're not using JIT (WASM doesn't support it) the runtime performance will be miles beyond V8 and JSC.
I think the perfect use-case for this would be to embed it in a application, kind of like GraphQL Playground. Not sure I'd use it for user-facing documentation though, as it seems it doesn't have SSR or HTML output. Docusaurus Integration would be nice for that reason.
Sadly, the problem I see with Bruno is that users migrating from competition are actually low-value targets and would never pay for anything. Regardless with what happened to Postman and Insomnia, they didn't loose any significant market share (again, only a certain minority, which would never pay anyways). Most of the people will just accept the new conditions and go on. It's not worth the hassle for them to migrate