I bought this to use with my Pioneer Premier DEH-P590iB, which is basically the same as the DEH-P5900iB sold here. I have it mounted in the 3 o'clock position, but have used it in almost all positions just to test it out, the only place it doesn't work is where the steering column completely blocks the signal (IR light.) If it's sunny, the IR light will be dissipated and may not work, but shading the remote usually helps. I've only had this problem once or twice in the last month and a few times before that, so overall it's a rare occasion that I'm traveling at that specific time of day in that specific direction that it completely blocks out the IR light.
The only downside I have with this is there is no pause button. (PGM on the standard remote) and if I'm listening to a CD or my IPOD, and get a phone call, I have to still use the original remote to pause the song. ATT works, but I listen to my music loud, and when it's on attenuate mode, it's still too loud to hold a cell conversation. It would also be better if it had an "ok" button (pressing the center of the round key on the original remote or the multi-function knob on the faceplate.)
The controls are intuitive and are quick to learn, each button is easy to touch-learn (you will be able to feel the difference between the buttons, rather than having to look at them) and the volume buttons on the back of the remote are large and easy to use.
I rated this a 5 because it is safer to use than the original remote, or no remote at all, and is way more convenient as well (especially when the loose remote falls under the seat and I used to have to fumble for it just to pause or ATT the song.)
It's easy to mount, but when I got my new car, the strap was cut to fit the old car, and is now too short for the new one. Zip ties or velcro will solve that though (hidden by my steering wheel cover anyways.)
I recommend this product to any one and everyone who has a compatible radio, and for those that don't, switch to pioneer, just so you can use this great product.