See this video.
I think it's a waste of money.
Change your oil on a regular basis _ that's key.
In the video the guy talks about an older engine become leaky and noisy.
This is so because the oil molecules in the synthetic oil are all the same size and smaller, where as regular oil are different sizes.
The bigger sizes fill the bigger spaces in an old engine keeping it quieter and less leaky.
There was a traveling salesman that had over a million miles on his Chrysler land yacht with the untouched bottom end _ ran like a watch with regular oil and all he did was change the oil and keep the bottom end clean. This was a long time ago when there was no synthetic oil.