Og, I think the Aquafx 3 stage is just RO, so it is fine to drink. If it is the 4 stage with di, you will get more conflicts. Some say yes, others no. You can also then tee off before the DI to drink the RO if you like. You can contact Marianne of Aquafx for more information. If you drink from DI, you may find a funny taste due the the resins, she recommends a post filter after the DI if you want to drink it.
The only concern for me is the flouride since I have young children.