Well, zee has only that steel part going for it, the rest of the mech is not quite durable enough and not only it can break but they also have tendency to bend from heavy use so they end up twisted (if you look from the above, the jockey wheels are not pointed straight forward but aim to the right. It's still the best bang for the buck, but let's not pretend it couldn't be improved after all those years it's been in production.