I use the brompton rack bag to carry a tool bag and it works very well. For my use case it's been worth the money. I can get 2 5lt tins of paint in it and have needed to quite a few times. The main downside is you can't stand the bike on the rack to park it temporarily when the rack bag is on it.
Ok so that box didn’t really work, has anyone had any experience of these ( or does anyone want to sell me a front or rear Brompton bag) H
https://bobbinbikes.com/products/box-bag?variant=13649733255216&gclid=Cj0KCQiA4aacBhCUARIsAI55maEqBuhMCbItMZKDegXGF1Ww8Q0quBcE0Sy3wYZOp8Jt0NrwV-Ujv0IaAow5EALw_wcB#fo_c=3179&fo_k=b803b9401635d4c2c2b30f8a42ba99f2&fo_s=gplauk