I bought this from the official website as I had a voucher. Anyway, the light doesn't actually ever wake me up by itself,and I can't bare to listen to the horrible alarm beep on it, so I dont use the sound part, just the light, and use my ipod to go off 5 mins after the 'sunrise'. Whilst it doesn't wake me up, I do think it is beneficial in that I don't feel as foggy or miserable in the mornings. I think it prepares my brain to wake up as it gets lighter.
The other bonus is that if you fall asleep reading it turns itself off after 90 mins so you don't wake uo at 4am with the light still on. However you do need to press the alarm button every night if you want a sunrise in the morning and this activates a sunset which is fairly useful too in getting to sleep although I usually have to delay it so I can read a bit more.
On the whole it is expensive for what you get and this model has very limited features, and the sound alarm is awful! I think it has helped my state of mind in the winter though.