It does not leave your oven any messier than roasting the chicken in a roasting pan
I roast chickens all the time, some are whole, some spatchcocked, and all are on a bed of onions, and lemons. Most ovens are self-cleaning these days unless you have an oven that is vintage, so really not an issue, except for cleaning the racks, of course.
When I first saw this method, I did try it and did not see much difference in it versus a regular baking pan. It does make for a fun presentation, however.