Considering that the Divine Might ability applies Divine damage to all creatures equal to the character's charisma modifier for the number of rounds equal to that modifier, it would appear that this feat is of little value. However, since Divine Might requires the Power Attack feat as well as a decent Charisma ability score to be useful, those with the Turn Undead ability that have either low Charisma and/or low Strength ability scores may find this feat somewhat useful. Considering the numbers of undead that seem to appear in AD&D modules and campaigns, such characters could find this feat quite beneficial.
As of Patch 1.06 this feat is more useful then it appears as the actual damage in game is 2d10 and it is a Free action meaning it can be activated while carrying out another action (ie: attacking ),it also stacks with Divine Might damage and itself if you choose to activate it multiple times in a round. So, for a character that focuses on charisma and has a lot of turn undead uses per day, this feat can easily turn the tide against powerful undead.