I've never played a moonkin past level 40 or so, but based on the screenshot that addon looks extremely similar to the default UI's eclipse bar. The only significant feature I see mentioned in the lengthy description is a prediction of how much eclipse power your current spellcast will add, but that hardly seems critical. If the addon were so amazing, either someone would have already updated it, or more addons would exist providing that feature.
Based on my experience playing other classes, I'd tell you that no addon will make you a better player. You've probably already read a guide telling you which spells to cast in which order, which talents to pick, which glyphs to use, which stats to reforge into, etc. -- now go figure out
why you should do all those things.
If you're using an in-game "rotation helper" addon get rid of that crap -- all it does is turn you into one of Pavlov's dogs, mindlessly responding to the flashing icon. Your DPS may suffer in the short term while you learn to play your character yourself, but in the long term you'll be a better player overall.
And finally, while fixing your DPS rotation is easy, what really makes you a good player is knowing what is going on around you. It doesn't matter if you're top DPS in the first 30 seconds of the fight if you die to every fire, cleave, and voidzone. It doesn't matter if you're top DPS if a tank dies and you're too busy mashing buttons to notice and throw out a battle rez (though you should also know how to assess the overall situation to know whether it would be a wasted effort). Trying to micromanage your eclipse power isn't really going to make a difference in the grand scheme of things.
