I must say that I guess I am the exception. I have used nothing but API kits since I started in the hobby roughly 4 years ago and I have never had any issues with the. I would venture to guess that they are the most used kits by members of the forum. As far as getting 3 pH readings ranging from 8 to 8.6, that could simply be a matter of the amount of time you wait before reading or a few extra drops of water in the tube. You don't have to be that precise when measuring pH.
The test kits are just a tool to make sure your parameters are in line. The only ones that are really important to know they are spot on are ammonia and nitrite. Obviously, you always want them to be 0. If you get a reading other than that, then it is definitely time to retest. If I go and test my pH right now and it reads 6.6, that's fine. Maybe if I ran more tests I'd get a 6.4 and a 6.8 but it's really irrelevant as to what the actual number is. As long as it isn't fluctuating severely up and down from previous tests, the fish will be fine.