The HIT is their refined CE. I believe it is replacing the CE and temporarily both are offered.
The HIT and M510-V2 are their newest updated triggers that tweaked some springs and geometry so that the sear bar would clear all the custom action cocking pieces without the dragging that had been reported in some instances.
If you are looking for a really nice trigger to work in the 1.5 to 3.5 pound range, the 510-V2 is excellent. If you want lighter, then the HIT is a refined CE that will go into the ounces and not have some of the issues the CE had in certain actions.
./