I use TI now, pretty exclusively. Having said that, there's always individuality in form and my current form is not pure TI but a blend of TI and my pre-TI form.

From a PT point of view, to make the TI form automatic you have to commit yourself to always practicing it. If you switch back and forth and change your stroke significantly when you switch, you form will suffer at both ends. It have to do with imprinting the nervous system with the right motor commands.

I would try to do all TI, understanding that when you don't concentrate as hard you will be swimming a combination. You will be slower for a while.