What are these tools for? I haven't been able to get much of a sense of that from their web sites.

My collection of papers amounts to about 1600 in 2.4GB, and I keep track of them by putting them roughly into folders for different topics, and maintaining a plain text file of minimal bibliographic details -- filename, title, URL, authors, and whatever notes I've made about them, sorted in order of addition to the collection, most recent first. Text search takes care of finding stuff. I use git to synchronise the library among a few different computers. I don't seem to have any need that any of these tools would be an answer to.

But perhaps there is a need that I do not know I have. If you were an honest salesman for one of these tools, how would you sell it to me?