I have actually come to prefer the all-castoring design. It requires more skill, but less force and the acheivable performance is superior. To turn a cart with fixed wheels, you must apply torque to the push bar. As well as being too narrow to give good leverage, the cart is quite dynamically stable and so resists this torque, so you must slow down or tolerate a wide turning radius.
To turn a fully castored cart, you apply physics - all you have to do is orient the cart so that is pointed sideways, then push hard. The key is then to maintain the cart pointing 90 degrees to the direction of travel throughout the turn, so that you can oppose centripetal force merely by pushing - no torque required. When the turn is complete, simply stop pushing. The cart will at this point still be oriented sideways of course, but you can correct this easily at your leisure.
To turn a fully castored cart, you apply physics - all you have to do is orient the cart so that is pointed sideways, then push hard. The key is then to maintain the cart pointing 90 degrees to the direction of travel throughout the turn, so that you can oppose centripetal force merely by pushing - no torque required. When the turn is complete, simply stop pushing. The cart will at this point still be oriented sideways of course, but you can correct this easily at your leisure.