Yes, it uses the ChatGPT website to an extent, similar to how hundreds of other extensions use the ChatGPT API, but it has features that make it possible to take advantage of the ChatGPT website in a manner that a regular human simply would not be able to.

For example:
1- ChatGPT does not allow you to toggle audio for your specific text, this extension allows for that by making ChatGPT repeat back user provided text and then toggling the audio accordingly
2- This extension allows you to choose the voices instead of going all the way to settings, making it easy and convenient for users
3- This extension supports sending large texts to ChatGPT and have it repeat back to you by splitting that text into pieces and sending them one by one automatically for the user
4- This extension allows you to download audio for your provided text
5- The extension allows you to have a good reading UI with a play/pause button as well as a playback speed option, which is necessary for readers

Now, some of these you can probably have the website do it for you, although it would take you a lot of time. While others, it is simply not possible without the extension like numbers 4 and 5.

So no, it is not just a "glorified shortcut", understand how something works as well as the value it provides before giving it such a rating.

Also, the pictures clearly DO NOT mention anything about in-browser reading, so make sure to read the description before using extensions.

To other users who might be reading this: in-browser will eventually be supported :)