I don't really understand why they call it "Italian School, after Raphael" but then go on to list three eminent critics who all agree that it is "Workshop of Raphael, early 16th century". Paul Joannides is an art history professor at Cambridge and has in 1983 published the book "The Drawings of Raphael", so clearly an expert. Konrad Oberhuber died in 2007, but is described at the Dictionary of Art Historians as a Raphael expert (he was director of the Albertina). "Bodart" is presumably Diane Bodart, Assistant Professor of Italian Renaissance Art History at Columbia University.
The drawing is based on Raphaels painting of the same subject. It dates from 1504, has about the same dimensions (31 by 27), and is kept in the Louvre. While the painting is larger vertically (and doesn't have the cut-off hooves for the horse), the drawing is wider and shows all of the dragon, not the somewhat awkward one of the painting.
It also has some differences compared to the painting, e.g. the tail of the horse, and the skull and bones on the ground. It would be interesting to see X-ray pictures of the Louvre painting to compare them.
The drawing given in Wikipedia as the preparation for this work is obviously for a different painting, the version now kept in the National Gallery in Washington. Still, it is interesting as comparison here.
Much more interesting is the drawing in the Uffizi. This is the same composition as the one for sale here, including the skull, the tail of the horse, and so on. The Uffizi version seems earlier, more searching, while the one for sale is more finalizing things, or simply copying the Uffizi version (though in any case a very good copy). The drawing is clearly not copied after the painting.
I'm no expert in Raphael or drawings, but when some of the most eminent Raphael experts claim it is from his Workshop, we have a link with a known Raphael painting and drawing, and the drawing for sale has a lot of quality and is in good condition, then the estimate seems very conservative to me.