Thanks for asking Don, I have had the same fears and had conversations with Stan (the designer/builder of FPT) from the beginning as I was very skeptical. He was very confident in his product and explained it in principle.
You have to consider that the steady rest must be tight so the engine doesn't rock or in any way be loose. Just like the original style. Then realize that one is "pulling" and the other is "pushing" against each other. They are 5/16" steel rod. And remember the engine actually is "sitting" on front and rear motor mounts as well.
I have had no issues yet, knock on wood. However, I run an automatic with a shift kit so I'm guessing that's less stress with shifting. I still wouldn't mind installing a safety chain or turnbuckle, link for some kind for insurance.
A L A N F R A K E S ~ Tulsa, OK