Hi Lsdium
This is actually my first post (bar intro) so glad it's going to be passing on some experience regarding something as interesting as tDCS. I bought a unit from a Chinese company (I'll pass the name on via message if you would like to know).. and have used it from roughly the last 3 years.
To be quick frank, I expected more. Thanks not to say that my experience is accurately representative of anyone else's experiences. However the descriptions of people using tDCS to increase their performance in the military and in other applications lead me to expect more than what actually happened.
The sensation is not painful or uncomfortable, apart from maybe the slightest stinging on the scalp where the electrodes are positioned. I used the most popular only brain-training platform in order to quantitatively measure the benefits/effects of using tDCS. Sometimes I actually performed worse, but then again, it wasn't exactly a scientifically stringent experiment I was conducting.
Overall I'd say that for me personally, that my experience with tDCS has been closest to useless, then moving towards beneficial, and not really at all negative or detrimental to my cognition. Others report significant benefits however, and so it's best (as always) to experiment yourself, because otherwise you can't really know for sure.