When you say all in one do you mean the arca is made into the bag or just one that can be attached and unattached if need be? I would definitely not get something that is made into the bag with no way to disconnect. Limits your uses. Get a plate and then a bag that can attach to the plate.
Here are some bags that will work on the Railchanger X
www.area419.com
Also some of the Warhorse bags can attach to it also.
www.warhorsedevelopment.com