I still do them, quite often actually. I cannot attest to whether of not I've gained anything from them, however I can state quite emphatically that as good as these feel any gains would just be an added bonus! To me the Twist feels more like a classic muscle stretch than that feeling that we normally get from stretching our penis. Additionally, considering how easy it is to do and the low impact nature of the exercise itself, there's really not much reason not to do them. I personally do them between sets of Supra's Slammers: Twist Left, hold for 3o seconds, twist right, hold for 30 seconds, Slammer with the left hand, Slammer with the right hand, repeat.
Oh, one other random note: When you get comfortable with these, try this: Get as full of a twist as you feel safe doing, then start kegaling like it's going out of style. You'll feel a hell of a stretch.
Glad to see this awesome exercise revived!
-Harm-