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If they're supposed to auto-stop based on liquid level in whatever you're filling, like a regular gas pump, don't count on it. Otherwise they're great. Only time I don't like them is for dumping into a car, spout is too short so it's just awkward trying to hold the can upside down and then they leak a little around the thumb button while inverted. Not exactly a normal use case though.
For dirt bike use, the 2.5gal ones are the bomb.