I have always been a big fan of Boost. I had a pair of the very first version and sped along to some PB's although the achilles was harsh and caused problems, Since then I ran the London Marathon in the first version of Ultraboost and another marathon in Ultraboost 19. Since then I have strayed from Adidas (although did use Reebok when they were owned by Adidas and they seem to get the foam just right) So, I was really looking forward to using the latest version of Boost. I have tried 5 and 5X but won't be keeping them as the lacing system doesn't lock down tight enough due to the insufficient lacing, the mesh gets stretchy and after fifty miles the foam becomes so soft it started to affect my back. For casual use, non heavy duty walking and for standing all day they will be really comfortable but for running there are a few more tweaks to be made - look forward to trying them when they are released.