The keys were updated for Lion in the more expensive one.
I wouldn't trust aftermarkets. For something you'll have for maybe years and years, spend the money, it's worth it. Not saying that Logitech, and whoever makes them aren't any good (they're great), but don't settle for cheap hardware, you'll never be happy and will end up buying a few that will equal in price over the long run.
The biggest issues that come with those will be connectivity and responsiveness.