Much like when car seats (or even seat belts) first went to market, as of now, there are no Federal Motor Vehicle Safety Standards that address testing a product like the Tummy Shield.
Sometimes it takes innovative products to inspire regulations.
Child restraints are regulated and as such all add on items are best tested for continued compliance with the testing standard. CPS techs use the general term “after-market products” to describe the products made to go in/on the car seat that were not built with or crash-tested with the child restraint.
The Tummy Shield has been crash tested so we know it works at least as well as just the seat belt though the comparison tests show us the Tummy Shield reduces the risk of submarining, while redirecting the belt crash force away from the pregnant abdomen. You can see video clips from the crash tests here.