Although Gorilla Marketing is attractive and eye-catching, do you think it has major effects on sales?

To certain extent it does have effects on sales but not major.

Guerrilla marketing was conceived to primarily target existing customers rather than new ones, aiming to increase their engagement with a product and/or brand. When selecting audiences for a guerrilla message, a group that is already engaged with the product at some level is the best target; they will be quicker to recognize and respond to creative tactics, and more likely to share the experience with their friends.