No matter who the kit manufacturer is, it is up to the builder to inspect and correct the airframe based on personal flying style and field of operation. This problem with FEJ is not new, I remember when SkyMaster was the subject of poor quality, and I experienced and witnessed flight control failures on more than one of their airframes. While I do feel the wing was not built well and the balsa grain surrounding the spar was incorrect, I also know that flying a jet from that field would add unnecessary and unexpected loads on the complete airframe in both the positive and negative g’s. In time the servos would have probably failed.