Magnet Configuration Comparison:
The E-type configuration is more efficient than the the U-type configuration.
To understand why this is so consider the two drawings below.

On the left is a cross-section of a U-type magnet and on the right is an E-type magnet that has been made by combining 2 of the same U-types.  If each magnet configuration is driven by a coil with the same ampere-turns then clearly the doubled-up magnet (the E-type) will have twice as much clamping force.  It also uses twice as much steel but hardly any more wire for the coil! (Assuming a long coil design).
(The small amount of extra wire would be needed only because the 2 two legs of the coil are further apart in the “E” design, but this extra becomes insignificant in a long coil design such as used for the Magnabend).

Super Magnabend:

To build an even more powerful magnet the “E” concept can be extended such as this double-E configuration: