Any good link describing the research? Ethics considerations are irrelevant for technology that isn't yet proven
http://download.cell.com/images/edimages/CurrentBiology/home...
which mentions "The long-lasting effects of TDCS, which can persist for up to 2 months" with a reference to this paper:
http://neuro.cjb.net/content/29/22/7271.full.pdf
This last paper is quite interesting, as arguments can (will...) be based off of it posing that tDCS does provide a long-term benefit. Unfortunately, the gain (in response time and accuracy) over a sham tDCS (e.g., placebo) is quite modest -- 15% with an error bar of 10% for response time, and 5% with an error bar of 5% for accuracy... Check the Figure 4 on page 5.
I continue to scan research in this area because I know that at some point there will be a recreational drug equivalent that runs off batteries. That is going to destroy a lot of wealth in the underground drug business. That will cause some violent changes in society.
As for TDCS I expect it to move along to the point where this may be like a calculator, not "required" but an accelerator for people with ones.
That said, I'm interested in a maker kit.