How it compares with Lua?

Strictly better unless you need an extremely small runtime rather than a very small one, or are exposing a scripting API to users who will recoil from prefix notation.

If you like Janet and Lua, might as well try Fennel, which was made by the creator of Janet.

I have read about Fennel many times and considered on trying it - I didn’t know that they have the same author!

This one actually has real arrays (mutable and immutable)