I find this website very useful to keep track of which games and DLCs I have, but there is one functionality I wish there was: adding all DLCs as owned. Unless it's there and I didn't see it, you need to add each DLC one by one, which involves two clicks for each.
Adding the checkboxes and the "edit all" which are already in the Collection page would be useful. More useful than the possibility of adding all platforms when you mark a game as owned. Is there someone who uses that one?