Testing under controlled combat conditions shows this spell only regenerates 3 mana every 2s for a total of 30 mana for the casters in its area of effect.
This spell along with Glyph spells and other creation buff spells are great to cast before a fight. As mana will start to regen faster while exploring, meaning you can often cast preemptive spells for free and they provide utility for your party.
ps3 Sometimes there is a bug where the spell stays active as a permanent buff until the character dies. The cause is unknown but when it does happen, the spell can stay active for a very long time. It is possible to save and reload the game with the spell active.
pc Confirmed on PC, unknown for consoles: The spell actually checks for resisting it(only on enemies). The bug is that the enemy is given the regen if the check fails and denied if the check succeeds. Allies automatically get the regen.