I do know that the master vertical switch has a much longer life, I was told one million cycles, but I cannot verify that. I too have wondered about the air lock hole. I never had any problem with my main sump airlocking for years, and it is very active. My seperate pump for the washing machine basin used to air lock often, and it was not used nearly as much. I do have air lock holes in both pumps now, but I would like to hear other opinions on that also.