Though its movement penalty is pretty hefty, it provides excellent Physical defense, and it's not very expensive to augment. Getting Fortified to level 10 is easy, and Body Fueling is useful on this vest as well.
Machine Assisted (on the pants and boots) would help with the movement penalty of -15% by increasing your movement speed, which if applied while wearing the Heavy Trooper Vest would decrease the movement penalty of -15%. In other words it will reduce the movement penalty by subtracting the negative 15% movement penalty, by the amount which a positive movement percentage gives off by Machine Assisted boots or pants from that value off the vest. Machine Assisted with the Dragonfly Pants and Titan MEM Sprint would shave off the penalty along with other items with movement bonus.
The official description for this vest states that this is the only armor rated with a full grade 7 for defense against physical damage. The description would need to be updated with the Hardplate Series debut.
The SAS seen on the Heavy class's Tough Body skill logo appears to be wearing this armor piece.