It's not a module, it is part of every new Redis version now. Well, actually: it is written in the form of a module and with the modules API in order to improve modularity of the Redis internals, but it is a "merged module", a new implementation/concept I implemented in Redis exactly to support the Vector Sets use case. Thank you for mentioning this.
I don't know what mid-sized data requirement is or how this is used in prod, but I have huge doubts that if performance is the need cost is the problem.
From what I've seen is fast, has excellent API, and is implemented by a brilliant engineer in the space (Antirez).
But not using these things beyond local tests, I can never really hold opinions over those using these systems in production.