I have owned a few. Currently I use both the Razer Nostromo and the Logitech G13. (Yes both . . . Lol!)
If you use either one you should be fine. The Nostromo "might" be better for your hands since it has an adjustable hand rest. Then again you could just move your hand forward or back on the G13.
Which one is better? I'm sure it differs for each person but for me they are very similar and I do not know which one I like better yet.
The G13 has more buttons, which is neither better nor worse, depending on what you do. For FPS I doubt you would "need" that many buttons. So in this case the G13 or the Nostromo would be more than sufficient. I would imagine you are also using a good mouse with a good button setup (off hand I do not recall the button setup on the Death Adder).
At first use you might "feel" that a gamepad is not worth it or is not intuitive. But you need to use it consistently and build "muscle memory." Once this happens everything changes and becomes MUCH better. Your fingers instinctively hit the right keys without having to look away from your monitor.
Another awesome aspect is learning and using MACROS. You can do so much. (I have a macro which launches my game, inputs my password and then starts it. In-game I can activate different types of macros to do many things, which gives some advantage.)
These gamepads can also be used for more than just games. Photoshop, video editing, web surfing, multi-media, etc.
There are profiles you can download, so sometimes you do not need to create you own. You can just use these and tweak them to your liking.
The G13 let's you save 5 profiles into it's memory, so you can take the with you, or have them available if you reformat your computer and forget to save them.
Razer has a beta product called Synapse 2.0 which basically saves all of your Razer product profiles to the "Cloud" so that you always have any and all of your profiles available. (Synapse 2.0 is in beta and I would guess that it will be available shortly.)
With both of these game pads you can save profiles straight to your computer.
If you have other questions, ideas, comments, etc., just ask.