The Gel Challenger is the more budget-friendly version of the GR line. They generally have the same outsole, maybe a tad difference in durability with the better is the GR. The products in the Gel Challenger used in the uppers and such are not as "top-line" as the GR. In my opinion, they feel very similar and are very close in terms of performance and comfort. The Gel Challenger is great for the value you get out of it considering how close it is to the GR.