I got this product with some trepidation as so many people complained about the back light. But at the same time, I saw so many bikers with these exact lights that worked fine. So I bit the bullet and bought these lights just around October when things started to get dark.
And immediately I found that the front light worked fine, but the back light didn't turn on at all.
But I contacted the seller through Amazon under "faulty item" and told them of my problem. They immediately sent me a replacement at no extra charge, which I was very impressed with (which is why I haven't down-rated them for the initial faulty goods). The new one works absolutely fine.
Both lights are good and bright, with the front one often acting as my torch when I go away from the street-lights. They have survived all weather conditions, including (but not limited to) hail storms, strong winds and the occasional knock when my inconsiderate house-mates knock my bike over.
So I am very please with this product, and would recommend.