Low-cost radio – MP3 + SD, pay attention to what?

I want to buy a new radio in my sad Nissan, which will probably be one again in two years with Mother Earth. Obviously I don’t want to invest so much. What I miss are MP3 capability and SD card input, which I unfortunately had installed in the old car and forgot to expand. My selection is as follows:Pyle Retroradio US import 2x80w 20€Tokai USB F 4x45w 30€Andersson CRA 1.0 USB kort AUX 4x40w 30€Dealextreme 4x5w 25€ What I don’t understand: Why does the latter wheel have io just a performance of 5W, where all the others have 40W per output? Isn’t that weird? What would you choose? At the moment, I only used an old Pioneer radio, which only plays radio and CD. I don’t use both.