To be honest, I've never been one for adding one more round. Not because if may or may not cause a malfunction. I just put the money I would have spent on the +1 conversion toward a extra mag. It's a training mindset for me as, if I needed a extra round for whatever reason then what the heck did I do with first 5-6 shots.
I carry revolvers exclusively now and I always get razzed by friends over capacity conversations. If I need it I should have been finding cover by shot 2 and moving, reload at cover. If I need 7 rounds I'm already in deep and in my mind better to have a fresh cylinder then 1 extra round.
I know this doesn't address you question directly, but food for thought and a extra mag normally adds more value to pistol vs extensions. Another view point is spend money on ammo that will do the job.