I have one. It does magic on old cells. I've even seen it bring dead cells back to life. I had some Sanyo HV cells that would not take any charge. I zapping each cell at 30 volts brought them back to life. When a pack seems wore out, a mild zap from this device nearly always gets the cells back to normal, or at least very close to normal.
Some guys zap their cells at 90 volts with this device. That will increase voltage at a noticable expense of runtine. One pack went from an average discharge of 7.10v to 7.2v, but lost about 800mAh in the process. For stock racing, a 90 volt zap might be helpful, but I would never suggest it. IMHO, it is just a quick way to kill an otherwise good pack.