Is it able to get rid of the grease in the hair?

Yes.? What’s hard to get used to....you only use about a quarter size in your palm start at roots massage in let sit 3 to 5 min. I color my hair so I’ve switched to nioxin for colored hair. I like it a lot as well as conditioner!

Do I wash my hair with my regular shampoo&conditioner afterwards ?

I wash my hair 2/3 times a week and yes I use this product everyone and I absolutely love it! I message it in my hair and scalp and let it sit in for a few mins then rinse. After my scale feels energized and refreshed and I get an incredible amount of volume.

Is this product vegan?

I don't think you can know this. For instance, it contains niacinamide. This is derived from both plant and animal sources. Good luck learning which was used in this product. Even if the maker of product thought it was plant sourced, certifying this is not something normally done. Should you be more concerned on the testing practices of the product?