An article was recently published on Nature giving a great overview on the current state of transcranial direct current stimulation (tDCS)—along with the context surrounding neuromodulation in general.
An important point this piece brings up toward the end—is the free-for-all nature of the current state of marketing for tDCS. Because tDCS is not an FDA approved form of neuromodulation, FDA regulations generally prohibit companies from marketing their tDCS products as being able to treat certain medical conditions—or having certain medical indications. This rule however is not often followed, with some companies clearing going as far as to claim medical benefits from their tDCS devices.
Companies in the consumer tDCS sector seem to span either ends of the marketing spectrum. According to the article, there are companies such as Caputron—the largest distributor of noninvasive brain stimulation devices—that are weary of this regulation and market their products conservatively, making sure to only offer unbiased information and no medical indications or claims to treat any medical conditions. There are other companies such as Halo Neuroscience that sit near the middle of the spectrum, claiming their technology can be used for performance enhancement and providing peer-reviewed publications to back up their claims. Finally on the other far end of the spectrum, the article points out companies like The Brain Stimulator, whose marketing actually references medical benefits—claiming tDCS has a high potential to treat depression, anxiety, PTSD, and chronic pain; although the website does include a small-print disclaimer near the bottom of the page.
You can find the PDF to the original Nature article here: