Well the only way you will have any visual indication of change is if you have visible oil sludge or varnish build up, then you will see how Auto RX cleans that up rather well. The other way to tell is by doing a compression test. If you have some piston rings that are not sealing correctly due to some type of build up or are stuck for that reason, the Auto RX is very good about getting in there and cleaning it and restoring compression. Also, if you have an oil leak from something like a front or rear main seal that is due to possible age or gunk build up then you will see the leak stop. Auto RX is very good about rejuvenating seals and such.
Ive told the story here before of how a co-worker avoided a $1500 repair job by getting a bottle of Auto RX from me. He had a rear main seal leak on his wifes Lexus and the Auto RX treatment cleaned things out and rejuvenated the seal and no more leak.
Other than that the only way to tell is to have an oil analysis history on the vehicle before and after the Auto RX clean and rinse cycles. It is VERY VERY good at what it does, but its hard to notice or see anything if you have a well maintained car. But it is good at getting vehicles with an unknown maintenance history up to par and ready to be taken care of.
