I've been using Planck (and Replete for iOS) when I need a fast-starting clj[s] REPL for checking things quickly. What would be the use case for Lumo for me?
The difference is that both Planck and Replete run on JavascriptCore, while Lumo runs on Node.js and V8.
One of the advantages of piggybacking on Node is that we get access to its whole ecosystem for free.