The belly button method can be used with any size of saline implants, because during the insertion process it is only a rolled-up totally empty implant bag which is being pushed up to the breasts through a belly button incision.
This method does have a few drawbacks. #1 since everything is being done surgically using endoscopic tools from an incision site 2 feet away from the breasts, it's difficult to construct the pocket with a lot of precision. This can lead to errors in implant placement, both vertically and horizontally, and is the reason that doctors will usually only work with round implants using the belly button procedure.
Second drawback is that, because of the same lack of precision, doctors have to be very careful about placing the implants close together in the center of the chest for fear of pulling muscle loose from the sternum (the dreaded uni-boob, "breadloaf" etc.) This usually translates into less than amazing cleavage when implants are inserted using the TUBA method.
However, the list of pluses is much longer than the list of minuses. No scars whasoever near the breast area. Minimal risk of nerve damage/sensation loss. Minimal tissue trauma thus faster recovery and lower risk of complications ...
My own implants were put in using a crease incision. This allows direct access for pocket creation and implant placement, and is the best for really big implants. It does leave some major scarring, but who cares since the scar will always be hidden in the "shade".