In battle i would use this to quickly block my opponents vision allowing me to quickly strike. Along with this justu i would use a justu that requires no handseals. To take advantage of my opponents blindness before he can counter. Stuff like Earth spikes, and my personal favorite lightning arrow step(Kumogakure custom) which allows me to travel quickly and strike in the same motion.
Remember the petals aren't real, so once the genjutsu is dispelled, so are the petals. He is blinded only when the petals block his eyes. The petals also suddenly appearing a key for figuring out it's a genjutsu.I would use this jutsu in short range. While my opponent is busy with it, I would use some taijutsu. The opponent could mistake this as the body flicker making it hard to figure out it's a gen. In battle, I would use it along with some taijutsu in short range. The petals mask my movement so I could always mask the use of hand seals.
( Genjutsu: Kasumi ) - Illusion Technique: Servant
Rank: D
Type: Supplementary
Range: Short
Chakra Cost: 10
Damage Points: 20
Description: The user does one handseal and throws a paper bomb at the enemy. The enemy, trapped in a genjutsu will see a clone of the user advancing upon him. As the paper bomb reaches the enemy, it explodes
So what you are doing here is altering your enemies perception of what the paper bomb is. (A paper bomb is just a small ball of explosive tags) He will see a clone of you approaching, instead of the bombs. When near, explode the bomb.