Once installed, this addon requires some fussing to set up correctly. You will need to configure it per role as it only applies to active abilities, but once configured you won't have to touch it again.
I tested this out of the box with my NecroLock spec. Here's what it looks like with no configuration:
To bring up the configuration panel, type /rbconfig
As you can see, it does not filter automatically based on whether or not a spell has a cooldown, so you'll need to go through and manually set everything up. You can ignore the non-GCD spells, but I filtered them all for thoroughness. I decided to pin a few longer CDs like Lich Form and Empty the Crypts, while leaving shorter CDs like Neddra's Grasp unpinned. Pinned abilties are sorted to the top, and change to a blue background when on CD, green when ready.
Up til this point, everything's going nicely, until I began casting again to see what the full effect was like. This is where the addon falls down.
Here you can see that Empty the Crypts shows as being on cooldown, with 2 seconds remaining, even though this spell is ready to use. The addon seems to be registering the GCD and applying it to any spell that is affected. Spells that are not on the GCD (e.g.: Lich Form) are not affected by this issue.
For unpinned spells, this problem got even worse: Grave Rot was being placed back on the list because of the GCD issue, even after its cooldown had expired. I tried removing all pinned spells to try it that way, and it was even more frustrating as spells that should have fallen off remained on the list.
Installation: 10/10 Easy. No errors reported.
Plug and Play: 5/10. You can use this right out of the box, but you'll definitely benefit a lot more by going through each role and setting up the abilities properly. It will take some time.
Configuration: 6/10. The GUI is intuitive and easy to use, but loses points for not filtering based on spells that have no cooldowns associated with them. It also takes a while to set up for each role.
Usefulness: 1/10. Tracking your cooldowns is vital, but for anyone who watches their CDs like I do, this addon will prove more frustrating than useful.
Overall: 4/10. This might be ok for certain classes, or to track specific abilities, but as an overall ability tracker it falls down due to the GCD glitch. The addon writer obviously put some thought into this addon, and the direction is good, but I can't recommend this for anyone who wishes to min-max their CDs unless/until the GCD issue is resolved.