I have found several hard-shell spinner (i.e., 4 wheeled) suitcases with brakes (e.g. from European manufacturers Delsey and Stratic), but have yet to come across any with soft-shells (that also have pockets on the outside for small items). Does anyone know of such a product, or perhaps could offer a reason why there is none (even for hard-shelled luggage there aren't so many to choose from)? Or alternatively, one with retractable wheels (where you can still use two wheels like you would a with a 2-wheel suitcase)? Another possibility would be a braking mechanism that can be purchased separately and used (fairly easily) on spinner luggage.
Here are some examples of hard-shelled spinners with brakes:
The brakes on the suitcases I listed (usually) just lock the two rear wheels, enabling the suitcase to still be pulled behind on the two front wheels, while preventing the suitcase rolling away when on an incline or on a accelerating/de-accelerating train.
I prefer soft-shell suitcases because they usually have outer pockets, which is useful for quick, last-minute storage and retrieval of smaller items. I also like the fact that they can expand slightly if you pack something bulky inside. Plus they don't break like some hard-shell cases do (of course they can tear, but that is usually different circumstances).
The advantage of a 4-wheel vs 2-wheel suitcase for me: The spinner can be pushed down a crowded aisle of a train rather than pulling it behind me (since it can be pushed in all directions it will fit down a narrow aisle better than the 2-wheeler).
I found that Muji once sold a soft-shell spinner with wheel lock, but it seems to no longer be for sale: