are there any disadvantages of using it?
Heena is most safest way to color your hairs but only problem with it is your hairs will become reddish after few days and again you need to apply heena. I would recommend it is better than any hair dye.
it is a natural hair color treatment so better use heena for hair color than other chemicals.
I use mehandi for hair color and I feel it is most safe method for hair color.