One major drawback for just coding the comfort roof option in the GM5 module is that it needs the signal from the key continuously. It seems that the signal is often not stable enough, causing the roof opening/closing to stop so you'll need to go back to the car to solve this. This will, of course, depend on the distance etc., but in general a "one-touch" option is more reliable.
I have bought the XCarStyle module for the roof, see link below. It is more expensive than the Gaptech module, but it also allows the roof opening and closing while driving. I find this feature quite helpful as you don't have to fully stop. You can set the maximum speed at which it allows opening/closing at 35, 45 or 55 km/h. The latter works fine for me.
https://www.dachmodule.de/verdeckmodule/bmw-469/bmw-z4-e85-cabrio-aio-modul.html