5mm works fine on barbs, just use a blow dryer real quick to stretch it over. I personally hate duotight fittings because they caused me to lose 2 kegs of beer and made a mess of my kegerator, but the EVA barrier tubing is cheap and durable.
I just saw the last couple posts on this thread. I'm in Valley Springs and just learning how to brew. Maybe if any of us are alive after Covid, we can do some kind of meet up.