We've started using this technique and I've used straight discharge as well as a hybrid "plastcharge" product from Wilflex. The straight discharge was a Jantex product, and the Wilflex was NF Plascharge mixed with a very soft white ink I had made. The results were very similar and I almost prefered the wilflex plascharge because it was easier to use, easier to keep the ink well on auto filled properly. The look and feel of the washed shirts were identical, even though the plascharge was mixed with a white plastisol ink.
We will begin using this for more and more jobs in the future. This process really shines on jobs that are 5+ colors on darks that should be printed wet on wet. Often times we need to flash after every 2-3 colors and with a 10 color auto, 2 flashes and a 7 color job, it's not possible without sending the job around multiple revolutions. With a discharge underbase, you can run the job like it was on a white shirt and print more colors wet on wet, and often times we haven't had to use the second flash.