Against natural disaster, better get cover under the pre-existing school desks than under very expensive blankets ! This will also be far more efficient against falling objects. Against a gunner, i don't think making all the kids laying on the ground waiting for a kill under their blanket is better than making them run for an exit away from the shooting ...

This seems well meaning but misguided. I haven't read stories on all the shootings but some of the worst ones were the ones where people got under their desks submissively and waited for their turn to be checked out.
I'm looking at a photo of $10,000 in security blankets taken in a room with a $200 wooden door. Of all the commentary I have seen on dealing with the shootings one of the best ones went into detail about the great lengths schools go through for fire prevention in terms of building design, construction, materials, and practice drills.
I remember attending a school board meeting for an 8th grade journalism assignment and one of the things that came up was the ridiculous costs of replacement light fixtures in the library because special fixtures were needed to meet strict code.
The number of school children killed in fires in a year has been aproximately 0 for years yet we lose numerous children to shootings every year but schools were never constructed with active shooters in mind.
The harsh reality is that the physical security of schools must be addressed even if doing it is expensive. At Sandy Hook the doors were locked but they were just glass so he just broke them and went through.
Imagine if the front doors had bullet proof glass and the classrooms had doors that served as proper barricades? The office monitoring the guy trying to get through the door could have hit an "active shooter" alarm that puts the school on lockdown and alerts the authorities.
Nobody wants schools to feel like prisons but they basically have to be fortified at this point and windows off the ground don't have to be barred or anything. Safely blankets aren't going to be enough and schools are already under funded for things like securing the main entrance.

"but the company points out they would still be a cheaper option than building dedicated shelters at every school in tornado-prone areas."
But a much better option. The shooter will start in one room. The sound a warning for all the other classes to funnel into individual shelters.
There is no time for any person to down their bright orange rectangular cape if a shooter wonders into the class.
Reinforced dead bolts and steel structure to the doors of classrooms will also help.

Am I the only person who finds it horrifying that kids get shot often enough that someone came up with this ?

So now a rampaging madman (does not need to be using a gun) can get free and plentiful bullet resistance armor for when the police finally do arrive.
That sounds like it is a good idea.

If a gunman can see a body part he or she can shoot it and the photos show how inefficient the blankets are at covering a body. The thought that school children have now to be able to escape from expected gun attacks is a very worrying trend.

Understand the American backstory. The critical step in "marketing", now, is bribing sufficient politicians to acquire regulations mandating acquisition of this paranoid crap by school districts.

@nicho It's something of an epidemic at this point and they only seem to be getting more common. Here is a chart of school shootings per year: http://i.imgur.com/Ti8JyHn.jpg
The source of the data is here: http://en.wikipedia.org/wiki/List_of_school_shootings_in_the_United_States
The graph was from 2010 but it hasn't gotten better.

Nicho, you are not alone in thinking that. It is a shame it seems to have come to the point where we need 'body armor' when kids go to school.
I think it would be better used a protection from the back as the kids run away from the shooter instead of just sitting there waiting to see if they will be shot next.
Perhaps with a tornado, they could use it in addtion to hiding under a desk chair or desk to shield them from debris?

The mind boggles!