no. Save your coupons for something that's harder to get or power.
you can farm Iruka easily through refinement under your ninja training. Once you have some 5* ninjas from shop such as Kabuto, Hinata, Sai, Lee. Recommended Kabuto, he's the easiest to spam with 10 points. Twice a day.

You'd probably have Zabuza, Guy, Yamato and Kurenai 5* over time. Don't buy them. They can be harvested through survival.