At the moment Catalyst is still in development and you can preorder it for a discounted price. All this means is that some of the modules may not function as intended, as they are still being worked on. If you are interested in this client now is probably a good time to buy as the client is close to finished but still available for a discounted price.
Some amazing hacks offered by Catalyst:
 Crystal Aura – This module has recently been rewritten, personally I am a fan of the rewrite, It added lots of settings and with a good config it is a powerful module.
 Kill Aura – This module has a decent amount of settings but I personally was not able to make a configuration as powerful as some other clients.
 Off Hand – this module has quite a few settings and was very consistent throughout my testing.
 Auto Obsidian – This module creates a safe hole around you, In Catalyst there are a wide range of settings and with the right config it is fast and reliable.
 Auto Trap – This module has more settings and more options than any other client I have tried, with a good config and low ping it is very useful.
 Hole Fill – this module fills safe holes around you to stop other players from healing.
 Name Tags – This module shows you what armour and items your enemy is holding, Catalyst has a very clean looking name tags module with quite a few settings.
 Obsidian Replace – this module replaces any obsidian around you that gets broken, this is helpful when players try to mine your safe hole.
 Hole ESP – Catalysts hole esp module is amazing, it is very customizable and looks really good in my opinion!