For me, the biggest issue I see with the example hamburger buttons there is that they don't look like buttons --- they look more like an air vent/grille, a stylistic thing rather than "touch here to get more".
Why do you consider that an issue, if I may ask? The generic nature of the button is exactly why I think it's actually a good icon, as it universally seems to mean 'tap this for more, but without completely losing your current context (as opposed to a back button, for example).
Any less-generic icon would not always be appropriate, and thus make this functionality less predictable.
Not that I think it's a good UX pattern, by the way. I'm just saying that if you're going to use a 'more' button, this seems like a better solution than custom buttons where you're not sure what they'll do.
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Why do you consider that an issue, if I may ask? The generic nature of the button is exactly why I think it's actually a good icon, as it universally seems to mean 'tap this for more, but without completely losing your current context (as opposed to a back button, for example).
Any less-generic icon would not always be appropriate, and thus make this functionality less predictable.
Not that I think it's a good UX pattern, by the way. I'm just saying that if you're going to use a 'more' button, this seems like a better solution than custom buttons where you're not sure what they'll do.