In regards to anything that could affect one's health, I trust science based sources rather than the website that brought you the "Eat a Tide Pod challenge". From the site I posted previously -
Although it is not harmful in small amounts, gallium should not be purposefully consumed in large doses.
That's referring to pure gallium which probably wouldn't even be terribly useful for any kind of trick, given that it melts into liquid at very low temperatures (29.8 °C - 85.64F). You have to combine it with other things in order to make it not melt immediately upon picking it up. Which almost certainly means introducing toxins into the mix.
Anything that goes into the mouth is at least partially absorbed into the blood stream pretty quickly, particularly liquids. I don't know what qualifies as "large doses" but considering it's got a warning against it at all, it's not advisable.