By the way, by holding sneak you can disengage the follow camera for a free camera. This is listed in the CDB entry, but not the repo due to time constraints. A duplicate readme.md will eventually be created - but due to a lack of time was omitted.
The experienced lag is due to Minetest's unfortunate inability to smoothly update the player camera. This isn't lag per se, if you were to look at the debug menu and view you frame rate, you'll soon realise this is an engine bug appearing as a performance issue.
The lag you are perceiving is due to the Minetest Client being completely unable to resolve frequent player camera updates. The speed is fine, and the entities were designed with hardware performance scaling in mind, and will perform the same whether the step rate is at 120 steps per second, or 4 steps a second. It is not for me to point blame if you're using ancient hardware to run more demanding games.
I published an updated package which fixes the nil comparison crash.