Thoughts on the companion bikeseat?

Here's the product:

http://www.thebikeseat.com/store/p3/Companion_Bike_Seat.html

Here's an article about it (I can't find any professional reviews):

http://www.thebikeseat.com/store/p3/Companion_Bike_Seat.html

I like the idea of being able to accommodate a passenger without having to buy a tandem or quadricycle or one of those huge cab attachments. I also like that the seat opens and has storage inside and it's lockable. I have a number of friends that aren't big on exercise or biking but maybe wouldnt mind me riding them around. Of course a few of them would be pushing the weight limit of this thing...

I have a steel framed mountain bike with pretty heavy duty schwalbe marathon tires... I'm considering getting one of these but I'm interested in the Chainlink's opinions here.