The massive hole there is that I don't get to interview anyone the company to see if I feel like its a good fit. I'm sure its saves them time but it wastes mine.
To be honest, it sounds like a net lose -- it's a definite negative for a candidate, with perhaps not much benefit for the company (high noise, high false negatives due to the awkward environment).
My gut feeling is that I would immediately reject any company that asked me to do that, if I had the choice.
And it's just a pre-screen, right? It's not like you have to make your decision right there and then if you do well in it.
I've already written a cover letter that responds to the points in the ad; if they can't prescreen sufficiently using that then they need to work on their ad.
Interviewing needs to be interactive because any decent job requires interaction.