I recently bought the B&R baseline "underseat" cabin spinner (the one that is not on sale for Black Friday at B&R). I will use it for the first time in December on a trip to Europe. Although I have not field tested it yet, I really like the bag, and it is pretty slick how it can ride atop my 26 inch B&R spinner that I check-in for the luggage hold...After my last trip in October, I decided I no longer want to carry anything over my shoulder again (in my late 60s now, too much shoulder pain) and this new bag will be my only cabin carry on, to hold just a few items like phone, charger, wallet/passport, and the Rx I carry on board (no more laptop or iPad for me). If it fits under the seat, great, but I won't mind placing it in the overhead, either.
In case anyone is still reading this, my wife and I recently used the above bag(s) on a recent trip to Europe and wanted to give my impressions.
Overall, it is a winner for us, did exactly what we wanted, It attaches and rides very easily atop our 26 inch B&R bags that we check-in and stow, for easy one handed rolling from the curb to the airport counter, and from baggage claim to exiting the airport. We flew on Delta, and it fits snugly in the overhead bin of a CRJ 900 for the connecting flight to ATL where we flew to Paris (in business class, easy fit in the overhead bins). Point being we never really tested the new bags for underseat storage, so I still can't comment on that aspect of the bag, but we really love these bags and will use them for all trips in the future.
The downside is the price, very expensive. But the bag is so convenient in the airport, making connections, etc. Never again will I carry an over the shoulder in cabin bag.