I know there's been complaints about Kass abusing presence of mind, but Ryze is a monster with presence of mind. 250 Mana from Mana flow band + 500 from PoM is equivalent to a fully charged tear. Other spammy champs with MFB + PoM is also a nightmare to deal with in lane as a fully stacked mage support spammer will whittle the enemy bot lane down before running oom. Just my thought on an underused keystone combo.
IN MY OPINION: The bad thing about PoM, along with the Hunter runes from the Domination tree, is that it heavily relies on takedowns. If the player is skilled enough to pick up those takedowns, and is skilled enough to push the leads from the takedowns, then go wild with this rune combo. But based on how I and others in my skill level play, we would struggle to quickly and effectively get all of the Hunter stacks/PoM/Mana Flow charges. I was talking more about the Hunter runes rather than PoM and Mana Flow, the Hunter runes requiring players to get a unique takedown for a stack makes it harder to stack than PoM and Mana Flow.
Before y’all flame me, you can do whatever you want. If you want to do PoM + Mana FLow then do it, I can’t stop you, I just want to share my take.
you only need 1 mana rune its efficent enough as it is. but yes it doesnt hurt getting both IF you got both the trees since your getting free money for mages like 
The problem with having both is you miss out of taste of blood and ravenous hunter.
