I don't think you don't need to use both, either one or the other should be fine.
If you plan on dosing by hand, once a day, I think the ABC+ would be easier. You just have to add one product. Just remember that you need to add it in a high flow area of your tank.
If you dose A, B and C separately it's just more work. If you are using a dosing pump the separate A, B and C are better.