I had a 550 gallon gravity fed system for years before I had any issue. I'd seen many other farmers with similar setups and they didn't have a containment system for a spill either. Mine worked so well that I quit running up the steps to turn the valve on and off each time I used it. The valve in the filler handle worked fine and never leaked. This was fine until the hose rotted through and failed right after the valve and filter outside the tank. What a mess! I don't have a clue how much money and how many hours that mistake cost me.
I now have that same tank sitting inside a containment tank on the ground with a regular 120v electric pump. Although the gravity fed unit worked fine, I have to admit that I like the 120v electric transfer pump with the auto-shutoff nozzle and all. I don't have to worry about remembering to turn the valve on and off and it's inside a containment tank anyway should a leak occur.
Other than the real possibility for a spill and having no containment system (at least I don't think you mentioned one), a gravity feed system will work fine for low volume. Many suppliers will not fill your tank, even a really small 55 gallon tank) if you don't have the basic EPA requirements covered. I think they can be nailed by the EPA should you have a leak and not have a proper containment system. At least that is what my suppliers have told me. Being legal with a containment tank pretty well eliminates a gravity fed system anyway unless you dig a pit around your tank and line it with plastic. My 550 gallon tank is still considered relatively small by most comparisons and the containment tank it sits in cost me around a hundred bucks or so. At least I'm legal now. Besides, the spill I had a few years ago was not only costly, but it took a ton of my time to fix. Good luck!