Actually, Dr. Brett Harris' counts are even more powerful than UBZII, but these are relatively unknown, and there is little documentation available other than from Dr. Harris himself. They can be found at:
Actually, this site is good reading for the theory behind unbalanced counts in general.
UBZII is more powerful than KO because it it is a level 2 count. Generally, counting systems can be divided into 3 groups: Single level counts, multi-level counts not requiring an ace side count, and multi-level counts that require an ace side. Counts in the same group are roughly equivalent in performance.
I have just about got a handle on UBZII - I booked a nice win at a couple of the local Indian joints last weekend.
However, the jump from level 1 to level 2 tags took a lot more work than expected, and I still tire more quickly than I did when using KO. I expect this to improve as I gain more experience with the count.