Do not uninstall your older cast extensions since the feature hasn’t been released for all. It will be, once Google releases a more stable version.
For those of you who have been using Chrome 51, checkout the new update from Google which has built-in options for Cast.
In order to cast, you could either click on the hamburger button on the right hand side of the browser or select a line in the menu that reads “Cast …” or you could just right click on a tab.
This doesn’t however mean that the old extensions are useless now. What it does mean however is that you are unlikely to need it in order to beam stuff to your Chromecast device. Either way, you could use it as a shortcut.
Do not be too worried if you are unable to find the feature, since the option isn’t available to everyone. Yes, this is applicable even if you have the latest, up-to-date version of Chrome. So, you may still want to hold on to your chrome extension.
The feature will become more prevalent, once Google release the stable version of Chrome 52, which will give you the power to mirror tabs into Google Hangouts.