The microphone is used for your voice control and the keypad is used for the stereo.
The Land Rover add-on PTI will use the built-in microphone and the vehicle speakers... the difference is that unlike the factory PTI, the keypad doesn't work and it's Bluetooth only. It's also missing the hardwired cradle option to allow phonebook integration (which has an external antenna & charging capability for the few compatible phones.) It's just expensive for the minimal features it offers.
A 3rd party solution will offer more features and cost less, but there is no way it'll integrate more than just muting the stereo while active. You can go ahead and try the dealer install PTI if your goal is to be as close to OEM as possible, but you may be disappointed.