Like the Mini-O this new bag is waterproof and has a roll-top similar to other waterproof bags you might have seen. My older O-bag did let the water in a little at the incorporated carrier block bracket, my newer one didn't. This new Borough Small is I can report - I was caught in a torrential downpour last week - as advertised completely waterproof. I do mean completely and include the small front zipped pocket.
The Borough Small is 30cm (W) x 28cm (H) and 11cm (D) and weighs about the same as the Mini O. A really useful feature is the two-way strap which allows you to use the bag off bike as either a shoulder back or backpack. Both ways are comfortable and adds a little versatility to proceedings. In addition to the two-way strap the bag has a central handle to use as well.
The Borough Small has a 9 x litre capacity with a front zipped pocket that happily accepts my iPhone 11, keys, wallet, energy bar, Oyster card... and more besides. Its main compartment easily holds an iPad and 13 inch laptop. At a push as long it wasn't raining it could accommodate a 15 inch laptop with just one side of the of the fastenings engaged.
The roll-top is easy to operate and and the small aluminium hooks are quick to engage and together with the wedding are heavy duty and will last years and years of heavy use.
A finishing touch is an air release valve on the front which allows you to empty the bag of excess air and make the package smaller. When I was carrying a big camera in it, I actually created a pocket of air in the bag deliberately to afford some cushioning which worked really well.
The Borough Small has rapidly become my favourite small bag and I would imagine the larger version of this would be as good for its intended purpose of carrying larger loads in a bag that is waterproof. For me it is superior to the Mini-O.
I know the bag isn't in orange or even go with anything black but I do like the blue a great deal. The Borough Small is such a good bag I don't care! You can carry small loads or much larger ones with the reassurance that the contents therein are kept bone-dry. I am struggling to find any negatives apart from the £85 price which may put some off. Definitely worth a close look if you have a Brompton and want a smaller bag up front!
Stay safe out there people!!