Only thing to watch out for is that they arent the squared off ones that fit in the Touran, any with a rounded bezel will fit, and if your looking at an RNS510 the easiest way to tell is based on the position of the SD card slot. Golf RNS510 SD slot is down the bottom of the unit, Touran SD card slot is on the left of the screen.
Could be the difference between the older and newer nav units, the MFD2 which is the older unit will have buttons along the bottom and isnt touch screen. The newer MFD3 (RNS510) will just have 8 buttons 4 on each side and 2 knobs, as this unit is touch screen based.
The other unit you mihgt be seeing is the RCD510 whihc doesnt have the NAV but instead has a 6 CD in dash multi-changer, this only has 3 buttons on each side of the screen.
MFD2
MFD3 RNS510
RCD510
And Touran RNS510, square bezel and different SD card location