Relentleserver is designed for server use and unsuitable for client use. If you aim to enhance your game performance, I recommend using my client-side performance modpack, Arcomua Modpack, which can greatly improve the framerate and other aspects of gameplay.
Relentleserver is a performance-focused serverpack that also includes management mods for server use. It is designed to quickly build servers with management features and good performance without changing the core gameplay.
Download mrpack-install from GitHub.
Open a terminal or shell in the same directory as where mrpack-install is stored (or add it to an environment variable) and type mrpack-install relentleserver [optional version number].

A carpet-based serverpack. Focus on lightweight and better performance with server management tools included.