you may find that with a handlebar bag that its a bit slower to get to the interrupter levers from the hoods lets say, compared to if a bag isnt there, a bit awkward.
I still have found it useful having them though when following someone and being on the tops already. just nice to be able to do a little braking here and there without having to move my hands from the tops.
I ride two dropbar bikes regularly, and both have these, so I've very much become used to having them and would miss them riding around with other riders, where I tend not to do really hard braking but "keeping a safe distance" sort of thing when taking it easy on the tops.