new ZEE brakes for me, very impressed after first ride. can't compare to new or old saints, but slightly more power than new xtr or formula one and less fade on very long descents. similar modulation to xtr, far superior to grabby formula's.
can't see a reason to spend more for saints, they seem functionally identical.
It's what you can't see that is the main difference, talk to somebody from Shimano, or a good Shimano dealer, they will explain the difference in the pistons, calipers, etc…
That being said, the Zee will probably be fine, but you do get what you pay for.