Thanks for reaching out.
We love John over at WPS. He is awesome. And he recommends those plates because they are super light-weight and awesome. It really comes down to whether you're on the ceramic or poly-plate train. :)
Poly is awesome. It's light-weight and is multi-hit capable. That's just fantastic. The Hesco 3810s with the ceramic/spectra hybrid is just a different animal. Poly plates tend to have trouble with higher velocity and especially AP rounds. The 3810 is rate for 6 hits with M855 (a standard issue, civilian legal, US 5.56mm round), while you have to go up to the Duritium GT to be able to stop those at all. however, the 3810s are also about a pound heavier than the III+ PA plates. Everything is a trade-off.
We decided that M855 protection is common enough we want that to be something that the armor we stock stops. We understand that mobility is sometimes more important than armor, though.
I hope this helps. Please let me know if I can help you with anything else.