Boots of Nondescription are particularly ordinary boots which will arouse no particular interest from anyone looking at them.
Anyone looking at a wearer of Boots of Nondescription will see the wearer just fine, but when they look away they will forget any and all defining features.
If asked later about what the person looked like, they'll say "err he was around... regular height? I think? And his hair was.. kind of a browny... red. Or was it blonde? Errr..."
If an NPC is wearing the Boots, don't describe the person or do a voice. Tell the players what he says in third person.
"Someone comes up to you and he says that he's got a message for a guy called Montgomery Fuzz. He hands a note and a dagger to you and walks off."
If a PC is wearing the Boots, people don't remember things about them.
Whilst this was intended for stealthy missions and such where having eyewitnesses would be bad, it can be used for other purposes.
Notably, my Goblin player drank a ton of mutating fountain water last session. She is now a horrific goblin-thing with a mushroom head and three-boned arms and poisonous insect-stingered back and is basically the most horrible thing in existence.
The townspeople cannot remember what it was that they saw, but they can remember the sheer terror they felt as they fled to their homes.