That works on packaging made completely of plastic. I usually just use a pair of heavy scissors to open them. Just the other day, I bought a wall wart (USB charger w/o the cord); it came in a bubble between a solid cardboard back and a cardboard front with a cutout for the blister. Sometimes, I can get a knife between the layers of cardboard, but if not, a sharp knife along the blister/cardboard interface will slice it open.
Still, a danger for all concerned.
Inspired by the post above I finally watched that short youtube vid.
Funny to watch her use the can opener wrongly and struggle like mad to hold onto the package and to struggle at the end to separate the partly detached halves. Had she tried to actually extract the item from the clamshell she’d have failed at that too; the opening she made was real marginally sized.
She *may *have a good idea. I’ve not tried it yet. But she sure didn’t demonstrate it’s ease very effectively.
Since everybody’s posting links, these are tin snips similar to what I use:
https://www.amazon.com/TEKTON-35103-8-Inch-Straight-Pattern/dp/B00KX4KAHG/ref=sr_1_5?s=power-hand-tools&ie=UTF8&qid=1479745378&sr=1-5&keywords=tin+snips
Basically very strong scissors that can cut thru thin metal, plastic, whatever.