Did you directly compare? On the MXR and the M400?
Haven't had a chance myself (also not in love with the chrome - hoping there will be a black option like the nimbus).
I will qualify any discussion on footers with YMMV
I also have not done any critical listening of M400s in my system yet and won't for a few more days. I do have more experience with Nimbus vs vortex on the MXR. I have about 9 sets of Nimbus and 3 sets of Vortex. I have found Nimbus to work best on assembled cases like the Ayre 5 series and Audio Research products. The Vortex works best on solid casings such as the Ayre R products. Since the M400s also have solid casing I am going with Vortex to start. Agree with you on the black but just like the Ultra 5s. You don't get an option