For those whose job or life circumstances involve route drug testing, the Arch Burger bun has both sesame and poppy seeds on it. Likely not enough poppy seeds to trigger a false positive for opiates, but better be safe than sorry.
On the extremely rare occasion I'm stuck eating at McDonald's I'll get a QPC and build it like a Big Mac with lettuce, pickles, grilled onions, and special sauce. In addition to being much better than a standard big Mac, they are forced to cook it fresh so you get a hot burger. I wonder if they would let you do it with Arch sauce, cheddar, and crispy onions.
I tried it. It was ok. I prefer the big mac sauce to the more ketchup leaning big arch sauce. The crispy onions were not particularly crispy. It is very large burger definitely a 2 hander. I wouldn't recommend thinking about grabbing at the drive through and eating on the way down the road.
If like ketchup on your burger I would guess you would like this one more than I did.