The Ball Zinger, Ballzinger, Ring of Power, ROP are similar things, originated from the Blakoe Ring (www.blakoe.com). Google these keywords and You will find a lot of informations.
The main purpose of these devices is to induce more testosterone production in some cases. Mainly in zinc deficiency (which is very common), it can help to boost the testosterone producing, which has a lot of effects: increased sex drive, gains in girth and balls, increased sperm production, more intense orgasms, harder and faster erections, solve some kinds of impotence, causes better mood and stronger muscles, etc. You will find informations about this also on the WEB.
Smart people found ways to make similar devices from U.S. pennies. Others use copper and zinc rods and some latex tube to fixing it to the balls. The base principles are the same: a light, steady current conveys zinc ions directly to the testicles. It is much more efficient, than the zinc supplementaries, wich should fill the whole body to the according concentration of zinc. (The zinc is essential to the testosterone production.)