If you've seen the Jack In The Box commercials promoting the imaginary Jumbaco, then you probably already figured that someone would end up trying the item out, even if it isn't actually on the menu. Sure enough, Serious Eats has gone ahead and tried it so the rest of us wouldn't have to.
Surprisingly, the review is pretty positive other than the fact that it is so messy:
Cheeseburgers and tacos share a lot of the same core ingredients, so the flavors blended together well (with the exception of the pickle)...The shell added some texture, and the two extra slices of cheese and taco "meat" brought a touch of simulated Mexican flavor to the burger, which is pretty mono-texture and bland on its own. On the downside, you need about one napkin per bite, and under no circumstances should anyone ever look at the slimy meat paste inside the tacos.
Now that you've seen someone else eat it, would you try the Jumbaco out?