Been playing more with this block the last few evenings, so a few observations.
Outside of kihon, if the block is thrown from wherever your hand happens to be, such as from the guard, it is pretty functional. There is already space between your blocking hand and your body so the block rising straight up from there is fine. Additionally, with the little bit of upper body rotation causing the punch to sort of glance off the blocking arm, you can quite effectively use your body to drive forward into the opponent.
When blocking and moving to the outside of the opponent, it is possible to press the outside of the attacking arm by moving in at an angle, hindering the opponent. The upper body rotation moving with the block does help with this as well.
The overall movement, again the rotation is helping a lot, makes it a pretty natural feeling movement to grab/hook the opponents arm and yank him after making contact.
Now from a natural standing position with arms hanging by your sides. That's where I'm still having trouble with this. I feel like you should be able to throw an effective block from this position. Without moving off line of the punch while blocking it's still an issue for me. Bill mattocks is right, you're trying to block a fist that's at full speed. You have to land the block on the wrist- there's no space to land further up the arm without getting hit if you don't move off line. It's all moot if you can move, but what if you can't?
There's elements to this block I really like, then there's some I really don't.
In sparring at least it's a non issue as you're throwing it from a guard. Not so sure about the surprise attack/self defense usage yet.