yes, it is
I dont have actual numbers for "What are the gains in heat reduction and longevity?" - but I can add they look better too
well - for longevity - they will last a heckuva lot longer than if you "header wrap" them - which is the only other option - if underhood heat is an issue.
and, for most of us - it is. the stuff which comes thru the firewall, does so mighty close to the 1-3-5 header. especially manual trans shifter cable.