DotVPN has browser extensions for Chrome, Firefox, and Opera. These extensions are easy to install and intuitive, with a visually pleasing interface. Unfortunately, many of the features they come with don’t work as they should — for example, the ad blocker doesn’t block many ads. DotVPN also has an app for Android and iOS (though they are buggy), but there are no native desktop apps.
ExpressVPN is my top recommendation for browser extensions. It has extensions for Chrome, Firefox, and Edge, and the extensions come with WebRTC leak protection, are feature-rich (and all of the features work as expected), and are very easy to install and use.