Thanks for the feedback. Gmail add-ons are only displayed when looking at a specific email message in Gmail. Google has their own add-ons (Calendar, Keep and Tasks) that are displayed when you're looking at your entire Inbox, but they don't let independent non-Google add-on developers do this. Our add-ons will only show up when you look at an email. This is explained in the window that confirms installation of any Gmail add-on, but it's really easy to skim or misinterpret it. I'll submit a feature request to Google to try to make things more clear. And I'll submit another request to allow non-Google developers to show add-ons when looking at the inbox.
To be more specific about where the add-ons are located: in Gmail web, the add-ons are displayed on the right side of the screen. In Gmail Android, the add-ons are displayed at the bottom of the message.
I'm sorry it's confusing but perhaps I can convince you to consider changing your review. Google does explain this on the installation confirmation screen. It could be more clear but, unfortunately, I have to rely on Google to make those changes.
I'd be happy to help if you have any more questions. Just reach out via email to support <at> conversantcommerce <dot> com.