The concentration of trace elements in these products differs. The concentration of trace elements in the A and K products is much higher, which means it's easier to overdose trace elements using A and K. The all-for-reef is more diluted, and in theory, all-for-reef is a gentler method of adding trace elements.
The recommended dose for all-for-reef is to start at 5ml per 100 litres and not to exceed 25ml per 100 litres.
The recommended dose for A and K is 1ml per 100 litres, with a big, bold warning in uppercase letters on the label to never exceed 2ml per 100 litres. This means it's far easier to overdose trace elements using A and K elements if not carefully measured or your tank demand isn't there. I always presumed trace elements were biotic organisms, and it's only through this post that I now understand that they are non-organic elements of the periodic table, containing metals. Adding too much to your water can have the dangerous consequences of eventually building up and, in theory, poisoning your tank.
I use all-for-reef to keep my alkalinity stable. I dose of 10ml per 100 litres, which keeps my tank stable at 8.5dKh. I have no idea how the 10ml of all-for-reef covers my trace element demand, as it's not easy to measure trace elements accurately. My last ICP test confirmed all my trace elements were fine, but I've now read even ICP tests can't provide accurate readings, making it very difficult to work out trace element dosing requirements.
With no way to accurately measure trace elements, who knows what to do? Sticking to weekly water changes is probably the best way to go.