(1) If you are an existing Blink customer, you do not need a second sync module. All you need is the door bell and you can simple add it to your existing account (as easy as adding an additional camera).
(2) If you are planning on hardwiring the blink doorbell to your existing doorbells wires. . . . you still have to use 2 AA batteries to power the camera. This did not make sense to me as I figured my hardwires would power it, but sure enough after calling Blink support I realized I needed to put the AA batteries in the camera. The hard wire will allow your blink doorbell to ring the doorbell in your home but will not power the camera.
(3) You can turn on motion detection or just have the blink door bell turn on when the door bell is rung. This is a nice feature. If you want to catch anyone that comes to your door (whether they ring the bell or not, you can simple turn this feature on in the app). If you want to save battery life and are only interested in door bell ringers you can turn motion detection off.
(4) It has two way audio, meaning you will always hear the person at your door. . . . but you can also choose to speak to the person if you choose. For me the audio the person at the door hears comes across a little staticky, but that could be my phone or the fact that I am using the corner mount.
(5) It has more of a fish bowl view so it catches a wide view (meaning it can cover most of your front porch)
(6) There is no additional cost to having the Blink doorbell or camera system. Unlike other door bell systems out there, there is no additional cost to the Blink Doorbell. The app is free, cloud storage is free, downloading images or videos is free, etc.
If you are looking to set it up with just batteries and no wiring to an existing doorbell system, setup is a breeze (will take two minutes). If you are looking to hard wire it, it is still pretty easy. I am not a handy man and what I know about electricity will shock you (get my joke) but even I was able to hard wire it. Get the doorbell, you will be glad you did. Hope this review helped.