I feel that QTing a fish will unnecessarily stress the fish out. In my experience with smaller numbers of fish in the show tank, it's less worthwhile to
QT the new fish than to add them directly to the main tank.
Basically, this is my experience. QTing is a problem. I've lost fish in
QT before, frequently due to water issues or stress from tank size. If I have a 25% chance of losing a fish to QTing but only a 5% chance of losing either of my two fish in the main tank because of adding a new fish directly, I feel that in situations with smaller numbers of fish (or less expensive fish) it's safer for everyone on the whole to avoid QTing.