I think the only issue is that a bottle is something you may struggle to get rid of later on, KWIM? IME MCHN's always seem to be obsessed with risk minimisation or something (which is so dramatically different to MWs!) - same with sleep "issues" - they recommend you don't feed to sleep because later down the track it might need to be changed and oooooooooooooohhhhhhh! How SCARY and HARD that would be! (Please note the sarcasm - difficult to put into a written post ).
As a PP has said, plenty of kids are still having formula bottles at 12mo. It's up to you as to when you get rid of the bottle. I am kind of relieved that my daughter has started to refuse the bottle while I am at work. Funny how these things happen - I don't have to worry about trying to 'get rid' of the bottle because she is just doing it for me!
So... to cut a long story short (TOO LATE!!! LOL!) I would agree with the others - stick with what's working for you until it isn't working anymore