Anything you fit will still allow LCD display to retain most of it's function. Temp, fan speed etc.
What you loose is the stereo displayed in the LCD, volume etc, but, you'll get a 7" to display that anyway.
Also, the steering wheel controls are disabled.
I know Kenwood have a steering wheel controller you can purchase separately for most of their H/Us. Soem other brands do also.
But really, how hard is it to reach the H/U?
The ebay ones, some of which do have full functions.
The one i have in my car can be operated by the steering wheel controls, and the station, volume and CD/DVD play time is displayed on the OEM screen.
Basically it is as if it was a factory unit.
Quality, well its still working 12 months on with out fault.
Sound quality, cant really comment, i'm no audio nut. Music is played, its loud enough for me, its clear enough for me
Unfortunately the unit i have is not on ebay any more. There are different styles. When i was looking, some worked with the oem screen, some didn't. So which ones work now i have no idea
think only the 2006 MPS had the lcd unit controlled by the headunit. easiest way to test it is to disconnect the headunit and see if u still retain the lcd. nearly all headunits will NOT display the audio part on the lcd, but who cares?
most headunits have the option to use steering wheel controls. look at pac-audio to see what headunits they support for the mazda 3
I've got an eBay one, there's no guarantee the LCD panel will work, everyone will tell you that, it's just depends on which year and unit is already in the car. Take out the unit, it takes all but 2 minutes and two screws, and if there's a wire from the LCD connected to a bunch of other wires then it will work. If the wire from the LCD plugs into the unit it will not work with aftermarket unit.
My previous sp23 and mps had/have the LCD working with all functions displayed. Except for the clock which you can't set but just unplug and plug back in at 12 and it works fine