I thought it tasted like quinine/tonic water or maybe grapefruit rind (the ingredient in the Beverly soda from Italy). Coin batteries sometimes have a bitter taste coating which is similar to the Switch cart.
I stuck just the tip of my tongue on there, and it was so bitter that it was more of a sensation than just a taste. Enough that I reflexively pulled away.
I was disappointed that it was a bit bitter, yes, but not in the category of “won’t do it twice”. Such that I even tried multiple cartridges. I’m retirement age, though, so maybe my taste buds are shot.