If you don't know that Harry can do previously unknown to the world wandless magic, than that might actualy not seem like a good trade off.

But Voldemort does know that Harry can cast one particular type of wordless, wandless magic -- he knows it because he taught him. Harry can end transfigurations. And he still has his glasses. Can Voldemort sense transfigurations that Harry is maintaining? If not, Harry could have a piece of Scotch tape stuck someplace it wouldn't be noticed, or a booger hidden up his nose, or a capsule up his butt like a drug smuggler, or a tooth, or a fingernail, or a toenail, or...

If Voldemort can't sense Harry's transfigurations, he should be operating under the assumption that Harry has a capsule up his butt that he can excrete and untransfigure into a deus ex machina. He doesn't need his hands to end a transfiguration, and he doesn't need his hands to poop. (If you prefer it to be a tooth, say it's a tooth. That's what Voldemort did.)

Of course, Voldemort doesn't seem to be the sort of person who would do that. He goes through the motions of being careful, but constant vigilance is not one of his strong points. And that's not, narratively speaking, a character flaw: if you think everyone else is a stupid NPC, you're not going to see a point in paranoia.

He should've kicked himself in the face as soon as he taught Harry how to do that. But he's not the sort of person who would.

Also, Harry should start carrying some transfigured teeth. A gun, a knife, and a broomstick, maybe? But I think I'm not being paranoid enough.