There are products that have been tested only to find they do nothing and there are products that are proven to be effective. However, I have never heard of a case where a legitimate additive "they do more damage in the long run" or caused any problem.
Here is my personal example of PRI as a fuel stabilizer/restorer:
I have a trailered 24' Robalo boat powered by a new 250 HP Evinrude E-Tec Outboard and a 118 gallon fuel tank. Due to medical problems I did not run the boat for 4 years and 8 months.
We wanted to take the boat out but had some concerns about the gas quality.
Many experienced boaters, boat mechanics and even Evinrude, told me to unload the old fuel regardless of what treatment I had used. PRI said run it! They were confident and explained how PRI is used in ocean freighters, large building emergency generators, etc. with never a problem.
So, we tried with the old gas. I was very surprised when the engine started instantly and ran as though the gas was fresh. We ran at wake speed, slow speed (approx 15 mph), mid range (approx 25 mph) and full speed (approx 40 mph) in the bay and on the ocean for approx 5 hours. Not once did the engine act up, sputter, hesitate or malfunction in any way. We also stopped and restarted several times. Each time, the engine started instantly, before the starter made a second turn. They were right, PRI works!