Hi philbo,
As a disclaimer, I have only very recently started trying ADD meds, so I don’t know that I will be able to speak to how beta blockers interact with, or counteract, the effects of stimulants.
I have, however, been taking a beta blocker for a few years due to an unrelated health condition called Postural Orthostatic Tachycardia Syndrome.
Also, I suffer from anxiety in the forms of social anxiety, obsessive-compulsive disorder, and just a more generalized and generally occuring anxious state.
They call me “Squirrel” at work. 
I haven’t noticed that the beta blocker has helped me with my anxiety. That doesn’t mean it hasn’t helped, just not to the point that I have noticed.
With one exception; I had a huge amount of anxiety concerning my health condition, to the point that I was suffering bouts of severe, acute anxiety that weren’t quite panic attacks, but were pretty close.
Having the beta blocker has helped with that, and I don’t know if that is because it helped with the anxiety directly, or because it helped with the tachycardia, which in turn helped with the anxiety.
Others may have had better or more noticeable experiences with beta blockers helping their anxiety. I’ve heard that it is used to help people with stage fright.
Good luck!
REPORT ABUSE