Mission requirements, weight requirements, and likey threats should usually dictate armor choice.
Hesco 4400 is a NIJ rated LV 4 plate. It is thick (0.9 in) and heavy (7.8lbs), but will stop one 7.62x63/.30-06 AP round. (very unlikely threat).
The U210 is an STR plate. A SAPI M is 4.2 lbs and .56 in thick. It is optimized for 5.56 and 7.62x39 including AP/BZ. It isn't tested for 7.62x51/.308 or 7.62x63/.30-06.
Personally, I believe the U210 would probably stop a .308 rd, but maybe not within BFD limits. I haven't tested it. Also personally, I'd go with the U210 plate 9.5 times out of 10. And the .5 is if I knew for sure I'd be in a gun fight against a .30-06.