Well how it works for me and DOES resume playing a folder i have in Media library.I basically imported a folder of a series i am watching and if I right click play on that folder in the VLC Media library it auto resumes that folder playback from the last episode and position i left it.I have installed Resume Media V3.40 and realise I tried it before. First the user interface is very obscure and I see no sign of it doing any more than VLC does anyway as it can easily be set to resume a playlist, atleast until you close VLC - I had given up last time I tried Resume Media. What may be the problem is that my playlist is stored in "Media" and can be copied to "Playlist" but this disappears when closing and re-opening VLC so nothing to Resume presumably. Nobody seems to know how to make a Playlist stay after closing VLC! All completely infuriating for so sophisticated a player otherwise.
In essence i dont so far have had the need to interact with the resume media interface.
I guess this extension may be a workaround with using Media Library,instead of a solution to keeping previous playlists you had in VLC.