If you want more player interactivity on your kart server (or an elo system that adapts kartspeed to the players average elo) then this addon is for you!
I especially recommend this addon for competitive servers, but it also works great on casual servers!
The rival music features can be a bit controversial seeing as it's loaded by the server, but it's done in a way to emphasize the rivalries between certain character choices and leave control to the owners of the game servers.
Rival music can be disabled in favor of a different music system, so it isn't too much of an issue. Really, it's up to your individual tastes.
If you put the effort into crafting music lists tailored to your character list and stages, you could make something magical with rival music.
Overall, I think these features are amazing. If you host a kart server, you can't go wrong with this addon!
As far as a HUD toggle, I can definitely look into making a client-side toggle!