I always loved their dead silent power tools.
The disguises were also a riot. A mask/disguise might work well enough for stage or screen, but I question whether you could pull it off in close quarters.
Tested on Mythbusters, you can't. The closer you get, the more obvious it becomes. There's no way they could pass close to a guard like they always did with them.
See the "Faking Out the Fans" video on the page for an excerpt: