The article warns about the possible hazards, but it's worth reiterating: http://www.theguardian.com/uk/2012/oct/08/teenager-stomach-l...
The nitro-muddling technique in L.I. is designed in multiple stages to prevent that from ever happening; for instance, if you shake a drink with LN still in it, you'll hurt yourself before you manage to serve a guest LN.
You're not wrong, though. You need to know what you're doing or you can hurt people. It's for that reason that we actually didn't play around with the stuff (freezing random stuff and shattering it, for instance); we just followed processes we knew would work.
Maybe I'm wrong and it's not that dangerous, but I don't think I'd do it if I owned a bar.
When chilling a glass, you dump out the LN. OK. That makes some sense. But then when making ice cream, you put LN directly into the bowl while mixing. Huh?
edit: I can see why you don't want to provide too many details. I will just say this story, while very interesting, terrified me.
As long as your food or drink are not spewing off large amounts of gaseous nitrogen, there should be no liquid nitrogen in them.
It's also easier in many ways for them. You don't even have to have freezers, since you're spot freezing everything. It saves you from buying a batch freezer for making it, which is $30,000 used. I'm told that if you're buying LN regularly, the distributor will hook you up with the tank at a low monthly fee. So it's probably much cheaper to start a stand that way.
The downside is it's a little less time-efficient. It's REALLY easy to make a 5 gallon batch of ice cream in a Carpigiani.
As far as dangerous culinary experiences go, the risk if you get it wrong is up there with eating blowfish.
Do not be tempted to do this as your first experience in handling liquid nitrogen. Get to know the stuff first.