Well, from what I have been hearing folks, true prl/pbl x TB are higher than regular mich, and can be just as high as the lower priced TB.
Here's the reasoning. High quality prl are solid colored. Take that quality x TB and breeders are hoping that new variations will pop out over the average crs breeding.
Now after having said that, I don't know if their theory will actually work- at least in the short term. Why?
I'll use the stack of cards analogy again, and although not perfect, it still gets the idea across. Imagine spending lots of time picking up playing cards and stacking them into a deck. Now imagine throwing that deck in the air. Some playing cards may stay together, while others fly off. You then need to spend time to stack those playing cards again.
The playing cards are modifiers. The solid coloration of crs/cbs isn't a mutation, it's from selective breeding from a bell curve. So take a selectively bred shrimp x another shrimp, and the modifiers (like playing cards) will be spread out again.
But yeah. The idea is they'll achieve higher quality TB with new variations.