‘tagging’ videos (works with images, too I think) is done with ‘sidecars’. It is basically a text file created next to the video:
London.mp4
London.mp4.xml
The downside is a small extra file on the HD you have to take care of when renaming / moving files. The upside is that the original file doesn’t need to be edited / saved.
You’ll need different software for that but I am not sure if suggesting competitors here is wanted, even if they are free.
But compatibility / connectivity is why I came back here, too. I have a small and probably easy suggestion. The fave button is fun and fast but almost useless, because it only works in tonfotos and even TF doesn’t find them anymore if a file or folder is renamed. Maybe you can add the option to optionally also write the tag ‘TonfotosFaves’ or something to the images? This way I could also find them in other applications or easyly again in TF.