I purchased a Porsche Classic Sat Nav system from my local OPC as i was able to get PCGB membership discount which was a bonus. Iv been using the system now for around 6 months and overall i am happy with it. The system is not perfect and for price you are paying there are better systems on the market at a fraction of the cost.
The biggest selling point for me was that it looked period correct and did not stick out like a saw thumb as is the case with all other aftermarket radios i have looked at.
Aesthetics, Sat nav with voice commands, Bluetooth (Spotify streaming), USB/Iphone charging hub,
Price, Sat nav screen size, USB/Iphone only slow charges, No DAB
One last thing to take into account is that you may need to upgrade your speakers and radio antenna as they maybe past their best. With regards to the antenna i believe you have to remove the front windscreen on later model 911's (i maybe wrong).