I do not know enough about electronics to know what they are delivering (AC or DC). I know the input is AC, but I don't know the output. If they are using AC, especially high frequency to drive it this could heat up the metal screws. Perhaps someone here will know more about electronics and figure it out.
Although the TENS unit you are using will still deliver an electrical charge along the nerves, which is what you want. So I would just stick to the TENS unit.
Sir if there any Chinese/Indian herbs if can use apart from above mentioned stuff.
I am sure there are, but I use a very limited number of Ayurvedic and Chinese herbs. So I am not familiar with most of them.