My eldest had to buy and use one this morning. Trying to get the safety spout out was quite a job. The gasket was a loose O-ring, and twisting the adapter into place seems to stretch it. The safety spout is spring-loaded--you have to twist and push the upper end of it back into the lower end for gasoline to flow. If your fingers slip and let go of the spring-loaded tip--it stops pouring immediately.
That's nice in theory, but remember that stretchy gasket. The can dribbled gasoline all over my hands.
I use an older version of such cans, that doesn't have a separate ring or a fancy auto-stop mechanism in the spout. That gets gasoline on me too.
If I'm going to walk away from the job with gasoline all over something, I think I'd rather it be a funnel than me. Of course, they're hard to get the dust out of when you're in a hurry.