I want to buy one of those night riders (diabetic related)

I'm so confused I want it to be a gift so I can't ask the person. I'm wondering if anyone can answer some questions about it. Like where I can get it... How much it will be if I have to buy them in bulk or is it a buy one and it's reusable? Because all the things I've read are a bit confusing. I was under the impression it was reusable...