I have tested this in trainer's and found out that Purify is still situational...
+2 regen per turn doesn't seem to mean HP regenerates by 2 points every turn.
It's just like a counter that stays on your health against poison. So, when you have +2 counter and the opponent plays poison (2 poison counters), the purify counter just negates it.
It's not like SoG. sorry everyone