I work at a company that creates software that developers use in their frontend. We have a free and open source version of our software and a paid, non-open-source version. It is easy to detect if a product uses our product (or not) and doing so doesn't require insider information.
We already have a section on our website that shows an image preview of client's products and links to their websites. This is done to promote those companies but also to show off what our product can be used to do. None of our clients have had an issue with this and some even request for their new products to be added to this list.
However, I don't believe that we have anything explicitly in our licensing/user agreement saying that we retain the right to promote websites that use our product.
Is it legal to make a video compilation of websites that use our product for promotion of our company? We would provide a link to their website like we do with the image showcase section of our website. We would only be showing brief clips of client's products, strung together for a short video. All products that we show would be publicly available and currently live at the time of making the video.