The smallest full size Transit is a substantially larger vehicle. It has a 3.9" longer wheelbase, is 5" taller, 5" wider, and 17" longer over all. Also the Metris has a 8.5' load floor versus the Fords 10', and about the same width between wheelhouses (dunno why the Ford has such a narrow track).
The Metris is, however, a much more sophisticated product, with such things as a fully independent rear suspension. Whether you need that sophistication depends how you drive. The Metris performs at speed maneuvers with ease that would put the Transit firmly on its roof (or, less firmly, the mighty Sprinter, for that matter).
Speaking of the Sprinter, the Sprinter Worker is the small Transit's competitor. It's cheaper than the Transit (when equipped with the mandatory diesel, since anyone in their right mind would take a diesel 4 over an old tech gas 6). It is 14" longer, 11" taller, although slightly narrower, on a much longer (14") wheelbase, but somehow cuts a better turning circle.