Overall, pretty happy with my Fast Ferment. I have made a dozen or so batches. I have started using it only for primary fermentation, however, and here's why, maybe someone has some ideas.
After primary, removing the ball and connecting a new ball for secondary, when the valve is opened to fill the second ball, the wort is aerated. I do open the valve very gradually and this helps.
The second reason, is that I find a glass carboy is better to visually inspect the batch and determine the clarity of the wort, instead of drawing off samples and exposing the batch to the air again.
Just my two cents.