Rob, I watched your vids and something doesn't sound right in your head set-up. In idle up mode you should have 0 pitch at mid stick and equal positive and negative pitch at high and low stick. It will be kinda difficult to flip and roll and fly inverted smoothly with +9 at the top and -7 at the bottom. Should be more like -10 at low stick, 0 at center, and +10 at high stick in idle up mode.
The servo wheel on your rudder servo looks a little small in the vid, I dunno how well the tail will hold. I have a Gaui 425, a mid-boomed 500, and a 550 and have the ball on the rudder servo out 13mm from center. Can't tell in your vid but it looks a lot less than that.
Are the fly bar paddles you installed smaller than the originals? If so, cyclic response might be kinda slow since it is even a little slow with the original ones.
Also, if in the future you are looking for some nice upgrades, a guy on our Gaui forum has some very nice upgrades for the Gaui 425/550. His "Easy-Mesh" motor mount is the shiz-nit. He also has new bearing mounts that accept larger bearings on the OWB shaft, as the small bearings seem to be a weak spot on this helicopter, and fail prematurely. His upgrades are under the name " HeadHunter Helicopters".