Flying Pigeon or Galavasana is one of my favorite arm balances. There's a couple of progressive versions of it and the pictures below show the full version of the pose with the back leg extended.
I had to retake the one on the right hours later as I wasn't fully in the original video frame. I wasn't warmed up in the picture on the right side--my arms aren't straight like the picture on the right which shows a bit better form. This is about a 7 out of 1-10 scale of difficulty for me. It's pretty solid when I'm warmed up and feeling flexible but if I'm not it definitely shows.
The pictures below show how I progress into the arm balance.
I usually stretch my hips and IT band (iliotibial band) before I do this and it helps to be warmed up obviously. I do at least 15 minutes of moderately hard practice to do this pose well. The picture on the right in the series of 3 is the less difficult and should be used as a stepping stone to get to the full leg extension shown in the top pictures.
Namaste