I was playing with one in the shop. I've got 7 of the black ones and I'm on the fence about swapping out.
The wheels are a little bigger and are less inclined to tumble a stack of systainers as you roll from carpet to timber, etc. The wheel is no longer on a metal plate, hopefully the plastic moulding is substantial.
They certainly lock-in to the systainer better.
Bottom line, I wouldn't hesitate buying then, but I wouldn't be in a rush to swap if you have the old ones.