I have read that the problem with the old-technology liners like Kreem and Caswell is that they break down when exposed to ethanol.
This form of alcohol is just about impossible to avoid in modern gasoline blends and it can be quite hard on certain polymers and other substances (including fuel tank liner coatings and older carburetor parts). Coatings like Kreme and Caswell's were developed before ethanol was in fuel blends - and their manufacturers have not kept up with the evolution of fuels.
I have had really good luck with POR15 - which is the stuff that Jay Leno uses on his big-buck car restorations. He even does testimonials for POR15 (see attached video) and while I am not
a huge Leno fan, I figure if it is good enough for his $2,000,000 dollar Duesenberg and Rolls-Royces, it is good enough for my $2000 Yamahas and BMW Airheads.