The downloads available on Informer pages are genuine. What you download has been verified by viruses and marked as safe. However, the software's license is not free. As far as I know, Camtasia is a shareware product which means you have the possibility to download and use it for 30 days as a trial only, then it requires purchasing in order to function properly.
To find additional information, use the official website of the application: https://www.techsmith.com/camtasia.html