Contrast of features on the sun is much better when comparing with the standard PST. I can recognize much fainter dark filaments for sure. But as far as resolution of images through the double stack filter is concerned, smaller features on prominences are blurred. I usually use an eyepiece of 6mm focal length with the PST, but with the double stack filter set up on the PST, I have to use 10mm instead for comfortable view because of the lower resolution.
This review was written in the old system and had content requirements that are different than reviews written today.