Fit my needs
I bough this cube to use it in my old backpack an ocasional use in my recently new Prvke.
It bits perfect in both. I used it with a minimal setup and have a bit of extra room:
If you have bigger lenses, you just need to relocate the dividers to suit your needs.
Even that, it is designed for the 21L one, it fits fine on the 31L. (It moves around a tiny bit but nothing to worry about).