I only see one although an important plus of such products - it's very easy to use and might be a good solution for older people who are not willing to learn how to switch coils, change cotton, refill etc.
But looking at it from a practical point of view, I don't really approve creating disposables which pretty well might've been made as a refillable devices. It's too much of a waste in materials + eco factor is important.
Also, regarding the advertising saying that 10M of these devices been sold worldwide, I couldn't find any merchant in the UK or even in China having them in stock already, found few saying "it's coming". Do you have any proofs you can share about selling that many worldwide? Who are your best sellers for this device currently?