Thanks to the very high level of correction most ED refractors have, the prism doesn't need to do much to "tweak" the image optimally. Something the glass prism can do, but a mirror diagonal can't.

It's really only been in the past few years that ED refractors with this optical formula have risen to great popularity. Just a very nice coincidence that such an inexpensive and readily available accessory can help them achieve even better performance.

If the data points keep accumulating to confirm that diagonal prisms improve image quality in a significant number of ED scopes (and perhaps other designs), this could be an opportunity for vendors to offer more star diagonals of the prismatic type-- especially better quality units.
More like the Baader T-2 model, but perhaps a bit less expensive. If there's competition at that end of the market, pricing should come down.

Finally, it seems to me that the term "right-angle star diagonal prism" is a bit of a mouthful.

Doesn't exactly roll off the tongue...

In the spirit of simplified nomenclature, I'd like to humbly suggest that from now on, such an accessory be called "the Clivagonal" (pronounced Clive-agonal).

Uhhhhhh, no good, huh?

Sorry.... never mind.