I'm by no means an expert but I rode my gelding in one with a plain snaffle bit, by recommendation from my coach. He was in one from the start as he had been trying to open his mouth and drop/fight the bit with his previous owner. He also had bit of a tendency towards a high head carriage/rearing and the drop helped us train him to a lower head/neck position. I never had any bit acceptance problems with him, ever. He was only just under saddle when I got him (wasn't started off correctly though) so I can't say much on how it affected his further training, but I definitely didn't notice any difference between him and all the other horses I was riding (all wearing plain or no nosebands). He seemed perfectly content and it definitely wasn't hurting him so we never changed it, as he was the type to always search for and test the limits. I sadly no longer own him, but he is still being ridden exactly the same - his bridle went with him.

Obviously the drop has to be correctly fitted for it to be comfortable, but if it is I really can't see any cons. It's definitely a much better try than a flash in my opinion while still addressing the same issues essentially.

Why are you looking to change?