I've never seriously tried off hand casting. I am sooo right hand dominant. I know I should try to learn because I can't fish the right side of a river as well as I can the left side. Being a lefty is an advantage in fly fishing.

Speaking of off hand casting, Jerry Seim, the rod designer for Sage casts every new rod design with his left (off) hand to simulate how the new rods would feel in a beginner's hand. He uses that to tweek his rod design to perform well for beginners as well as experts. I thought that was an inventive way for a very good caster to test his rods.