If you are thinking of buying a laser comb then I would suggest you do a lot of research into how it works. The theory may be there but so far there have been no scientific peer reviewed studies that can show the affects of the laser comb or the laser brush. Often times it is cited that the manufacturer has FDA approval. Approval and certification are two different things.
If something is approved that just means it won’t do any harm. It is like saying dumping a glass of water on your head is approved for hair regrowth. It isn’t going to grow any hair but it won’t hurt your head either.
The only way I would purchase a laser comb is with a money back guarantee. And it should be from a reputable dealer.