They probably haven't tried it because if you try something that you aren't completely sure of, you might mess up somebody's brain. People do make mistakes and the more complex, the more trouble it brings.
I am not sure I understand your statement.
The company has been around for some time
tDCS has also been around for some time and is actually not complicated at all and there are several DIY projects:
http://www.diytdcs.com/ although they are not as polished as the focus device.