Well, I have no direct experience with them, but I know some guys don't like the foam because they say that it will eventually degrade and then little pieces will clog your fuel filter. As far as size, I'd say the bigger the better especially if you want to ride all day long out in Moab. The red rock desert is a pretty lousy place to run out of gas. That's about all I have to offer on the subject.
'78 Cherokee NT in GA
'79 J10 Golden Eagle in UT