So I saw it and did buy it!
SA pointed out to me that with the organizer inside the St Louis will sit up on its own, rather than collapse, which is nice. I also like that it matches the St Louis interior. It fits inside my old Fidji and actually makes that bag look nicer when carried since it tended to fold in half before. It doesn't fit inside my Artois, though, perhaps mine is smaller that the one that enjoy1 has.
It barely fits in my Dior Book tote (though I have a Dior pouch that I use inside of that). It is nice inside my Loewe
basket bag, before I didn't like carrying a lot of loose things around in that. And of course it is useful if I decide to carry Louis Vuitton Neverfull and other random tote bags I have. I can squish it into the Chanel Deauvlle but it makes the sides bulge out a bit.
Overall I'm happy with purchase!