Honda has an opinion, I think he is misleading.
Festo QS series ARE rated at -.95 bar and work perfectly well, even using a medium, kerosene for which they are not designed, unless mistreated. Reread the Festo data sheet, it's quite clear.
I have 12 jets in my fleet, ALL have Festos in the suction side, none leak. My BVM F4 is in its 17th season, still with the original fittings. My 2 BobCats are about 15 years old, ditto! My FC Mig 29 has a myriad of Festos for the twin engine installation and in the hydraulic system, no problems.
The main fuel outlet of the main tanks on my two Airworld Hawks are fitted with Festos. I often remove the tube for de fuelling. Each season , I cut the tubing end to refresh it to ensure a fuel tight connection, never a problem.
It it does not make sense to condemn these fitting s because one or two guys have had problems. Bit like those who condemn Tygon, which, when correctly used, works perfectly!
A visual check for the amount of air in a hopper tank is a good, but not infallible, function check for leaking connectors.
David.