On my classic cars from the late 60's /early 70's, I use an additive Millers VSPe. It is said to provide valve seat protection, raises the octane rating by 2 RON, and, more importantly, provides protection against the harmful and corrosive effects of ethanol on older engines. I have use the Millers product (it previously was just called VSP before the need the protect against ethanol) for 17 years. It is based on a manganese formula, which in tests carried out in 2000 when leaded fuel was banned, gave it better results than other additives based on different chemicals.
I tow with my classic cars, and don't have any pinking, have not noticed any valve seat wear (valve clearances closing) and fortunately have not seen any issues from ethanol, as unlike more modern vehicles, cars from the 60/70's had components in the fuel system that are severely effected by the relatively high amount of ethanol in modern fuels.
I'm a bit sceptical about these so called pellets in the tank. Comprehensive tests conducted by motoring organisations have dismissed the claims of these pellet manufacturers as to their effectiveness.