Jeff,
The thoughts are the ball links are certainly valid. The first weekend I flew it, they loosened up a bit and the trim was all over the place! So I zapped them in place. If they keep moving over time, I'll replace them... I had them new in the package and nothing else on hand at the time ;-)

Tim,
It's a lot easier to install them with the body of the servo in the fuse. You don't have to cut a big hatch in your stab and the 3421's just slide right in the slot already cut for you. It took me about 30 minutes to install both sides. ok, maybe closer to an hour, but it was easy!