Question about Arlo Smart Hub Add-On Unit

Yes, it should work. Here is the full compatibility list: https://kb.arlo.com/000062284....
The price surcharge on the plan has been quite a foolish move. That's why we went for the base as well. At least you have that option and you're not forced to get the plan. Yes, you can watch the videos via the app. There are also push messages when motion is detected. However, recorded videos cannot be watched directly (no preview), but are first downloaded to the mobile when clicked. What still works is the direct connection to the camera via app (live image). Positive side effect of the hub: noticeably better WiFi connection to the cameras than before via home WiFi.