I have used it at the initial stages of my tank with great results, however when I had more and more corals (mainly sps) the demand grew and it stopped working for me. it was very difficult to dial in especially that AFR contains calcium formate which needs up to 48 hours to be broken down in order for any changes in the kh to be registered on a test kit. so lets say for example you accidentally overdose, you will only know after many hours which is too late in my opinion (been there). The lack of control on individual components makes it very difficult too.
In conclusion, it is PERFECT for tanks with a low demand but I wouldn't use it on a high demanding reef.