The pros are that they could (not will, could) dissolve something that your fuel additives weren't. The cons are that they are basically mineral spirits that are sold to you for about a 1000 percent markup, and probably aren't needed in the first place. E10 is going to mix with them just like any petroleum distillate. As far as I know they would do nothing to mitigate the bad aspects of ethanol (oxidation and water absorption).