Well, I've not done a scientific study, but every single person I've ever communicated with who was on pre-mixed did not have good control. They struggle to maintain reasonable levels unless they eat exactly the same thing at exactly the same time of day every single day, which isn't practical for many people, and they also experience a lot of lows (for the same reason.)
There are many on this board and others who take a basal insulin combined with a rapid and have excellent control. I think it just depends on how involved one is willing to be in managing one's blood glucose...how often one is willing to test and correct, if necessary.
Ruth