I started out wanting to discuss just Ratings Buster.. but I see from my screenshot, you’re actually getting a five-for-one-here. The screenshot is showing Equipcompare (the tooltips side-by-side), TankPoints (comparing this item to the worn item in terms of tanking), HealPoints (compare this item to the worn item in terms of healing), AuctioneerAdvanced (the vendor prices) AND Ratings Buster.
Equipcompare falls into my Tier one addons (critical, existence is painful without this). Everything else is Tier 2 (this makes my life easier .. alot).
Ratings buster shows the numbers.. like translating +18 int into 0.25% spell Crit, +6.9 Dmg and +6.9 Heal. More specifically it also translates “ratings” into percentages (17 crit strike rating = 0.77%). At the bottom it also shows the summary of the stats of the item.. and on the not-currently-worn item, it shows the difference between the two items.
In the above, Timewarden’s Leggings would give me 150 additional health.. but I’d lose quite a bit mana, holy damage, healing, and mana regen. That’s why Timewarden’s Leggings is in my tanking set and Starcaller’s Plated Legguards is in my Healing set (currently worn).