Our adapter has WiFi and Bluetooth hardware. It connects with Bluetooth and sends the WiFi credentials to the phone, then disconnects from the Bluetooth network. It works solely on WiFi from that point on

Yes, it works every iPhone from the 6 (running iOS 7.1) all the way up to the 14 Pro.

You can use either phone, but if you have both in the car, it will connect to the last paired phone.

As a plug-and-play solution, the CPLAY2air is very easy to install.

Turn on the Bluetooth and WiFi networks on your phone.
Make sure your phone is not connected to any other WiFi or Bluetooth networks and remove the hands-free connection from your phone and car system settings.
Plug the adapter into the CarPlay USB port.
Wait for the interface to appear on the screen.
Click the search button.
Select the phone you want to pair the adapter with (or connect via the Bluetooth displayed on the screen).
Select "Pair" on your phone when the notification appears.
Update your firmware (see firmware update instructions).

Connect your phone to the adapter and wait until CarPlay appears on the screen.
Enter 192.168.50.2 in your browser and click “Go.”
If you see an update available, click it.
Wait until the update bar reaches 100%. 
When CarPlay reappears on the screen, you’re done!

It depends on your phone and car, but it usually takes 7-14 seconds.