I have one in my fn2. Is great bit of kit, you occasionally get a little interference if using a iPhone but its not noticeable when music is on, just in between tracks, i like my music and have it on pretty loud often and sound quality is suberb!! It more depends on where you get your music from, I use spotify and iTunes and have never had any sound issues.
Getting to the back of the stereo isn't too difficult, more time consuming trying to get the bits of dash removed to get to the screws securing the stereo in! There will be a guide on here I would of thought! Only advice is be careful when prying/pulling the top part of the dash (above the stereo) off, it is defo only clicked in but I broke a clip pulling mine up with too much force at too much of an angle.