I used this product on my hair during the summer, and I found it to work amazingly well. I have naturally quite dark hair, and yet the jelly lightened my hair by many shades. However, it did not take it past a natural looking colour.
The dye has a pleasant smell about it, and so your hair does not smell all day, also it doesn't make your hair fell dry or brittle, on account of the conditioning oils in it. It works well, though does take multiple applications and lots of heat to start to see the colour changing.
I found that you have to stop using the dye before you reach your desired shade as your hair naturally lightens in the sunlight, and the dye can leave your hair looking brassy, if your hair was dark to begin with. The dye can also damage your hair slightly as it does have hydrogen peroxide in it, and so you should follow up with an intensive repair conditioner.
Take note that this is a permanent dye, and so if it does not work well on your hair you could end up in the salon paying to get it re dyed.
This dye works best on natural "virgin" hair, and also on light hair. If you have darker hair I would recommend giving this a go as a lightening treatment as it works well and wont take you too far away from your natural colour.
All in all I found it to be a good product which I have used multiple times, and feel that if you want to lighten your hair progressively then this is a good way to go. It is also good for first timers as it is not as damaging on your hair as most other dyes.