The term "buffer" applied to these products annoys me. Generally they are straight Alkalinity additives. The notion that your chemistry is "buffered" is misleading IMO. Sounds like a safety measure when it is not. We care about stable Alkalinity much more than "buffered" pH.
I believe you're best with "balanced" supplements like commercial 2-part or DIY 2-part additives. Avoid anything that calls itself "buffer".
2-part is works well in most cases. Ca/Alk/Mg dosed separately also works but requires more work, more testing and can easily result in less stable water chemistry. I think it did in my case anyway. I started out dosing RedSea Ca/Alk/Mg supplements separately and testing each one weekly. Now I use TLF C-Balance 2-part additive and recently only measure Alk. When I test all parameters they are always in balance. Coral growth took off exponentially after the switch to 2-part. Of course it may be different for others...
Apex monitors my pH, which tends to stay 8.1 - 8.3. High 7's is also OK, generally indicating excessive C02. The fix for that is to get fresh air into the tank or skimmer if possible. Or use a C02 scrubber. Raising Alk to get higher pH is like the proverbial "cutting off your nose to spite your face".
-droog