I just enlarged a picture of my grandson (3 1/2 yrs) scaled by 4X which came from instagram. I used the GPU (Radeon RX580) with high memory but tried both the Max quality off and on. With it off I saw some artifacts around his face (red lines, etc) but with Max quality on, they were mostly gone. So at least in the case of portraits, Max Quality = yes seems to be the best choice. Face refinement was on in both cases.
Great to hear! Feel free to share the before/after images