There is a remarkable about of downplaying the seriousness of a firewall and the penetrations through it. For starters, check your sources, a TSO C53a hose, the kind that carries fuel, must withstand a 5 minute direct application of a 2000F flame 5 inches away for 5 minutes. The firewall and all fittings are rated for 20 minutes of something similar. Now, like I said, older airplanes are what they are, copper tubing or TSO hoses behind the panel for fuel and oil, no shoulder harnesses, single vacuum pump with a lazy turn and bank indicator for the backup. You upograde them to newer standards when you can.
But the justification for adding an uncertified fitting in a safety-related function becuause its "easy" or "looks spiff" is inexcusable. The rules are there for safety, and once you know about it, you know. A grommet with some Permatex red silicone will burn through in less than a minute. This fitting is good for a couple minutes longer. Usually you are more than one minute away from a suitable landing site. Its your plane, but your passengers donrt get to make the same deliberate decision to, or not to, compromise their airplane.
from: https://www.aopa.org/news-and-media/all-news/2006/january/01/airframe-and-powerplant
What's the difference between fire-resistant and non-fire-resistant hoses? A fire sleeve. There are two types of fire sleeves — the slip-on and the molded-on, or integral. The minute a woven fiberglass slip-on fire sleeve is properly installed over a rubber tube or Teflon tube hose, that assembly becomes fire resistant. Slip-on fire sleeving has a bright-orange exterior while the integral sleeving is colored a rust brown. TSO C53a requires that fire-resistant hose assemblies be able to withstand a 2,000-degree Fahrenheit flame applied from one-quarter inch away for 5 minutes.