The very first thing, of course, is to download the AddOn. I'll admit that I was apprehensive about the RazerNaga Addon because it was simply a custom version of Dominos, an existing action bar mod. Between Dominos and the popular Bartender4, I had more experience with the latter. I was also extremely wary of a peripherals manufacturer handling an AddOn ironically because I'm concerned it wouldn't be updated -- I'd sooner trust the open source community to keep things current. However, Razer Community Manager Travis Wannlund, aka Razer|Mjolnir, assured Mike Schrammduring BlizzCon that Razer would "do their best to keep the AddOn updated".
As I'd mentioned, customizing one's UI takes quite a bit of planning, particularly when dealing with powerful action bar mods and even more so when changing one's entire playstyle. Installing and activating the RazerNaga AddOn is easier for players starting from scratch. The very first dialog box that players will encounter is a prompt asking to "sync" the RazerNaga buttons with current action bars. If you don't use any custom key bindings or use the default UI, clicking 'Yes' should be quite alright. Otherwise, click 'No' and configure it using the AddOn interface. Below is Razer|Fakesteve with a tutorial on how to configure the RazerNaga Addon.
After a bit of stumbling, I found that the Razer's proprietary mod was every bit as powerful and customizable as Bartender4 for my purposes (the RazerNaga AddOn is not compatible with Bartender4 or any other action bar mod, so these should be disabled). Considering I probably didn't maximize Bartender4 as much as I could, the RazerNaga AddOn eventually allowed me to create a UI that was nearly identical to the one I had using Bartender4. Players activating the AddOn for the first time might find that their bars will have been completely rearranged:
Don't panic. It took me a few moments to sort things out, but once I got my bearings I was able to slowly configure my bars to something less cluttered. The AddOn is too powerful to be discussed in depth in this review, although Razer's tutorial video should give a fairly good idea of how it can be customized. It's possible to show all bars at once -- not recommended -- or to have one main bar that "pages" according to different conditions, which is how I set up my UI. Each action bar can have up to twelve buttons and set to have different key bindings and modifiers.
Starting virtually from scratch, I was able to shift most commands from the N52te (or keyboard), and almost exclusively to the Razer Naga, leaving my keyboard hand for modifier keys and other functions such as targeting. It's important to note that when configuring the AddOn, it's set to the same toggle as the Razer Naga, whether it's set to the Basic  or Advanced [NUM] mode.
Because they have the same creator, the RazerNaga AddOn is very nearly identical to Dominos with the exception that the former has toggles that sync directly with the mouse, automatically setting all the keys to match the built-in keypad. Toggling the "Always use Razer Naga buttons" option will map the action bar from 1 to = in Normal mode or N1 to + in Advanced. More experienced users can opt to assign custom key bindings to each button.
The AddOn is capable of quick paging, or showing different action bars at the press of a button, or what Tuller, the mod's developer, calls "bar mirroring," which shows a different set of spells on the same action bar when a modifier is pressed or certain conditions are met. This is actually less confusing than it sounds, and when you get the hang of it, you will actually want to take advantage of it. The RazerNaga AddOn also supports certain bar "states," wherein the action bar changes according to conditions -- stealth, bear form, combat, out of combat, etc. The possibilities are pretty extensive, and players able to maximize the AddOn's features will squeeze the most of the Razer Naga.
In the Razer introductory video, Razer|Fakesteve mentions that most players got used to the Naga's controls within the first 18 hours of gameplay. This might sound a bit long, but considering how much time we can sometimes spend playing the game, it kind of makes sense. Most of my hours have actually been spent configuring the AddOn... getting used to the 12-button keypad is secondary. Muscle memory will follow in time, so the keypad isn't much of a concern for me (Razer has also included "trainer" stickers, adhesive bumps that can be placed on certain keys) -- it's customizing the interface to take advantage of all the buttons that's the real challenge. The great news is that the RazerNaga AddOn works as advertised.
I've currently set up my Death Knight, Hunter, and Shaman UIs to work primarily with the Razer Naga (with pet controls on the keypad) using the RazerNaga AddOn while my Paladin still has a mix of controls on the N52te and the Razer Naga using the Bartender4 AddOn. I remapped the Razer Naga's forward and back buttons to be mouse buttons 4 and 5 using USB Overdrive, a shareware app for the Mac. It's still a work in progress and after hours of gameplay I still find myself rearranging my spells according to usage and accessibility. After experiencing the Razer Naga, I'm inclined to migrate completely to its custom AddOn on all my characters and like the Zen student who must first empty his tea cup in order to learn, I'm going to throw everything out. The Razer Naga is the kind of device -- no, the kind of weapon -- that demands it.
What's epic: 17 buttons, with a 12-button cluster that's easily accessible with the thumb. Excellent hardware specs far beyond what typical MMOGs demand. A proprietary AddOn built to integrate the Razer Naga seamlessly into the World of Warcraft.
What's vendor trash: The forward and back buttons beside the left mouse button are hard to reach. Some buttons can be confusing to press because of the cluster (e.g., keys 5 and 8).
Equip it or vendor it: Equip it, definitely. The mouse is responsive, with the keypad buttons having just enough resistance to prevent accidental presses. Razer's decision to complement the Naga with a custom AddOn was brilliant and is what makes an already great product into an epic one. Players able to take full advantage of the AddOn and the Naga's arsenal of buttons can effectively elevate their gameplay to a whole new level. Or, as Razer's marketing guys would put it, Get Imba.