I thought press checks were to make sure the gun WAS loaded, not to check to see if it is UNloaded.While external extractors do sometimes prove useful, would you pull the trigger of your gun if the extractor is smooth instead of sticking out without checking the chamber?
If you're trying to verify that the gun is unloaded then you need to visibly inspect the chamber. I'd suggest that a press check isn't sufficient in that case but I'm not going to argue the point.
If you're checking to ensure that a round IS chambered then checking the extractor will suffice. The only way I could imagine this would give a false indication is if the chamber is loaded with an empty case--which, BTW, a press check would also fail to detect was empty.
If the gun doesn't have an external extractor or a chamber loaded indicator then I guess you're left with no other option but to press check.