A good teacher has to figure out where you are, where you need to go, and how to get you there. If you are simultaneously studying with another teacher, the second teacher will have a different assessment and idea of where to take you. Therefore, every time you study with each of your two teachers, you are traveling in different directions.
You may be happy in thinking that you are getting the best of both worlds, but your divided focus will be very frustrating to your teachers. You will probably never know, but when your best teachers get tired of seeing you go in different directions, they will give up on you.