Radiant Synergy, the third paragon path feature of the Instrument of Wrath, is similar to the 7th-level Weapon Specialization class feature of the slayer and the knight, which grants them an additional benefit whenever they use their power strike encounter attack power.
However, unlike Weapon Specialization, the benefit is not fixed; instead, it depends on the battle blessing that the Instrument of Wrath has invoked when he uses smite of radiance or pulse of radiance. In this respect, it is similar to the psionic augmentation mechanic introduced in PH3, but without the flexibility (and, some would say, problem) of allowing the character to trade off more frequent augmentations for (theoretically) less powerful augmentations.
This mechanic was, in a way, previewed in the daily attack power blessing of might, which the radiant avenger gains access to at 9th level. All daily battle blessings have this mechanic, and this paragon path feature provides similar benefits for the at-will battle blessings.
This paragon path feature increases the complexity of playing the character since it effectively provides two additional, potential effects for each at-will battle blessing. This complexity is mitigated somewhat since the additional effects are usually related to the base benefit of the battle blessing.