Earlier quoted context omitted.
That's a dropshipping site for AliExpress products shipping from China. You'll save money if you buy the product straight from AliExpress without a middleman in between. However as you said, the toothbrush doesn't actually work.
Is there a general way to tell if a site is (likely) a dropshipping site?
Read the terms and conditions, privacy policy and other more "obscure" information like that. Dropshipping items always ship from China and returns are received to a warehouse in China.
In their Terms of Sale, Sonic Brush mentions that it is rebranding the following product "We are selling the following brand mark : W-White.". So this would be the dropshipping product they buy from AliExpress.