There are a few disadvantages of Google Duo:
-It uses your phone number as your ID, which can be inconvenient for users who want to keep their phone number private. This also means that you can't use Duo without giving out your phone number.
-It doesn't have a lot of features compared to other video-calling apps. For example, it doesn't have a screen-sharing function.
-It doesn't work with over cellular data, only over Wi-Fi. This means that you can't use it if you're not connected to a Wi-Fi network.
-The video quality can be poor in some cases, especially if you're not on a strong Wi-Fi connection.