Didn't use my usual dose of 2so last fill up, and noticed a new hum from the engine. Refilled and added my usual 2so dose and gone is the hum. Even if there's no other benefit, that alone is worth the extra 25 cents this treatment costs me per fill-up.
I believe I get slightly better mileage aswell, but that's harde to judge than the noise. Doesn't need to improve much to save 25 cents though, if the average fill up costs me 72 euro.