Purify breakthrough just increase the stats when you purify your equipment. The only time you should you do it is only when you are willing to spend a lot of money since the only time it is available, you'll have to spend a lot. It doesn't give out a lot of power in my opinion.

You can get iruka in two ways. You can get him in events or you can refine fragments when you have 5* ninjas.

Purification pill as a goal itself is ONLY when you have maxed out everything. Ammount o power you get through a single pill is abysmal. Lets imagine dream scenario, where you have lv10 refinement on an item and all golden purifies with 100%, which in total gives you 665 ini/crit/combo/injury/control and the same 665 via purifies, so a total of 1330 stat. Single pill will give you 13,3 of each stat, which results in like 30 power increase. 30, considering u have all golden 100%, which is pretty much unobtainable.

Since it requires (at least so far) always either 30/40k recharge/spend, it's ok if its an addition, but not as a goal itself.

Okay, so you guys recommend me to use when I have all golden stats on that particular equipment?

I'm no quite sure but I think kabuto, sasuke and kimi give the most refinement points so in that case you should aim to 5 star them asap in order to piece Iruka faster. In fact you should 5 star all the sr trial ninjas because they're all equally useless but more accessible for frag refinements.

I have hinata and kankuro five star is that good?

It seems like you don't understand what we said. Purify is the last thing you want to focus on but that is going to happen if you spend thousands of dollars on your power. Just don't worry about it.