I bought a pair of these for my wife for Xmas. The basic problem is that the seal between the two halves of the light is totally inadequate, which means that if you submerge the product as shown in the picture, it begins to ship water straight away.
The result is that it works well for the first bath, poorly for the second, and not at all by the third. Both lights have filled up with water, causing the batteries to emit loads of brown gunk which has clogged up the switches.
A very poor quality product, which shouldn't be on sale at all. I'm sending mine back for a refund.