Andy said the AndyMark wheels would be back in stock within a few days, it sounds like they are waiting for parts. Look at the comments and watch the video I linked above.
I personally trust the AM wheels more as we used them on our robot last year without issue and I don't really trust plastics at critical points on a robot. I would consider a wheel a critical point. Last year we used some plastics on other portions of the robot and by halfway through the season we switched out for machined aluminum parts.
Even with the improvements, I would still be hesitant on VexPro mecanums. I would rather wait and pay for a product that I know will work based off of experience.