These prices are ridiculous for something you still have to cook. In many parts of the country they are easily as much if not more than an equivalent meal at a diner or similar establishment, even including tip, and of course much more than any fast food joint. I could see this as a complement to one's regular eating strategies (whatever they may be) but not a replacement, which is apparently what is being sold but not what is marketed. You get three or four meals a week out of 21. The other big failing is selection. I'm tempted to try it out for a week, but most of the services don't even tell you what you'll get and only one or two offer exclusively vegetarian options.
Still, if one of these companies slashes prices in half and offers a wide selection of food that can be selected a la carte, I do think they're offering a service that is quite valuable. Until then, it's mainly a curiosity at best.