To talk to your points specifically:

1) A silent room is a room that is paying attention. All too often, when observers are behind the mirror (or tv monitor) they start discussing what’s going on. Sometimes this discussion is positive. Often it’s derogatory to the user (“Oh, what kind of idiot is this?”). In either case, the team has stopped paying attention to the user and is now in their own world, doing their own thing. Important things could happen in those subsequent moments and the team would not see them.

Instead, I encourage the team to pass notes, which participants have no trouble ignoring. When a team member is writing or reading a note, they also aren’t paying attention. But the rest of the team is, so most of the information is still being retained.

The other advantage of having the participants in the room with the observers is a single facilitator can make sure both groups are getting what they need from the session. When you have a separate room, either you need two facilitators or one side goes without the facilitator being present.

2) With regards to the ethics:

We use full disclosure for the participants. They know why the observers are there and the observers are trained to behave respectfully. Having done this thousands (literally!) of times, I’ve never once had an observer act inappropriately in a session.

One could argue that having an unknown group of individuals behind a mirror (or tv camera) that the participant doesn’t see or know why they are there could be unethical, since the participants are being observed without their full understanding.

I wouldn’t knock the method until you’ve had a chance to try it. A lot of people have had similar reservations to yours, however, once they try it, many of them decide it’s an ideal approach that solves many of the current problems with testing.

Jared