I have seen them in person, and yes they are huge. Ask Error what his opinion of them is. He owns a set.
Personally, I think they are too big. Too much rotational mass. Too heavy for jumping. Just, too big to make them anything more than a show piece.
Now, that being said, get yourself a much more powerful engine (he runs a Hyper 8-port which is no slouch) like something larger than a Picco .26, something on the order of a .70, and those tires might be worth their weight. But as it stands, the .21 - .27 engines are just a little underpowered for those tires.
A good alternative to the 40 series tires by ProLine are the Jumbo Maxx series by IMEX. Their selection of rims is not very robust, but the tires are the same size as the 40 series. AND you can jump them.