Over the years I have owned several small jig saws. Frankly it was always a love-hate relationship for me because I tend to compare cut quality against band saws, even on jobs I could never do with a band saw.
Back in 2006, when I fell into the Festool spell, I did not use any jig saw often, so I did not even ask my Festool dealer for demonstrations. Then in 2009 a project came along that would be ideal for a jig saw. By then I had seen a video about the European method of using the jig saw below the work, for better view of the blade. That featured the Trion PS 300 EQ.
My good luck was the time I drove to my dealer another customer was buying additional jig saw blades. My dealer mentioned that the other customer had owned a PS 300 for a few months. I asked if he had tried the method of holding the saw below the work and rotating it on the knob. That customer asked if he could demonstrate doing just that. Upshot was he came to my condo (this was before I had a shop) to coach me in the use of the Trion PS 300.
With the jump start having coaching from an expert, I approached the Trion with confidence.
I have never had any problems with a Kapex and I currently own and use 2 of them. The Domino is so different from any other tool it did require more practice and experience. I have never felt there was anything wrong with the Festool design or construction quality. Since I have used a Domino most days since buying one of the first sold in Los Angeles, I have coached several nice folks about them. I learn something from everyone I coach.
My gut feeling is there is significant miscommunication about the Carvex. Since as far as I know the Carvex will remain NAINA, I have never tried to see one in action. Why jigsaw techniques that work with the Trion would not apply to the Carvex is unclear to me. Yet reading these posts I get the impression perhaps some coaching of the new owner would have helped. Never having received any Festool product with a shipping defect, I still cannot discount the possibility the OP somehow got a bad Carvex. I have faith Festool will make everything right.