Knowing what I know now, if I were to start over, I would start with Open and stick to only Open.
As you said, no other division comes close to Open so for me, switching back and forth to iron sights and the dot would slow down my progress in Open. If I would only shoot divisions with iron sights, then I don't think that would be a hinderance in progressing to a higher class.
Switching guns may be fun but I'd rather be good