I've been looking around for a Gillette Super Adjustable. I often hear not to get the one with the plastic base. Though, I don't know how to recognize it. Those that offer it on ebay certainly don't mention it.
I don't think the plastic versus metal makes much of a difference to performance, and after 30+ years of use the plastic ones haven't broken yet so I'm guessing they're pretty sturdy. Personally, I wouldn't stress over it.