From discussions I've had with several Jetcat service guys, it's not that the vectored nozzle is the issue, it's the strain that is placed on the bearings when doing tumbling or high rates of rotation in off-axis manuevers (i.e. tumbling) that the vectored nozzle makes possible. Makes sense as a turbine wheel turning 120K or so is going to act as a pretty good gyroscope, placing a lot of loads on the bearing races and cages/side walls.

Barry