What are the key differences in performance and durability between the Adidas Terrex Agravic Ultra and its predecessors, and have Adidas effectively addressed the issues with the previous models in this latest iteration, particularly in terms of breathability, grip, and overall comfort for long-distance running and trail cycling, and how do these shoes compare to other popular models from competitors such as Salomon and Hoka One One in terms of overall value and performance, and what are the most significant upgrades or changes in the Adidas Terrex Agravic Ultra that would make it a worthwhile investment for serious athletes and outdoor enthusiasts.