K.I.S.S.
The simpler the system, so long as it still works, the better.
More complicated multi-level systems are not only more mentally fatiguing but also lead to more mistakes.
WIth hi-lo, you can almost do it in your sleep once you have enough experience under your belt.
The only *slight* improvement would be to go to the Uston count, which counts 3-7 as +1 instead of 2-6. I have NOT made this change because of the learning curve and because 30+ years of habit makes the change a bit difficult, which I would expect to lead to mistakes. Also, Uston converts RC to TC on half decks, where I've got converting by full decks down pat -- another change of a lifetime of habit which could lead to confusion and mistakes.