I just started using it. I am seeing better gas mileage (1mpg, 8.1L gas GM, now up to 12mpg highway with Mobil 1 synthetic oil) in my truck, stable in my car (108K miles, V-6 Mazda with Castrol dino oil). As for parts inspection, well, I have (knock on wood) no plans to go inside any of my motors anytime soon.
I also put it in my boat motors in the fall, but have yet to try it out (496HOs with Mobil 1 synthetic).
It does get VERY thick in its own bottle when cold. I don't know what it is like when diluted with oil. I had to heat it up in the oven to get it out of the bottle to add it to my car during a winter oil change (had been stored in garage).