So I just got Unyielding Sentinel for my level 20 (now 21) Favored Soul. I thought it was a cool choice for my 2 weapon battling Favored Soul. But so far, I'm disappointed.
The skills, despite them saying otherwise, are not regenerating. Though I assume this is a bug.
My biggest disappointment is the way that Turn Undead and Smite Evil are implemented. Basically since I didn't start off as a paladin, and these skills grant the actual feats, and not a new ability, the damage done at level 20 is pitiful. It isn't worth it. The damage done on a smite is (7+ (3*Paladin Level)). Since the paladin level is low in a non-paladin picking Unyielding Sentinel, the extra damage on a smite is laughable.
However if a level 20 Paladin were to pick Exalted Angel, that Paladin would have access to a smite ability that is keyed off of total level, and not Favored Soul level.
So here is my suggestion. At the very least, the "Effective Level" for Smiting and Turning needs to be Total Level / 2. To bring it into line with Exalted Angel, it should be just Total Level. This could be accomplished through new abilities, or a modification of the Smite and Turning feats themselves.
Otherwise there is no benefit for me picking Unyielding Sentinel over Exalted Angel for my Favored Soul, even if my FS is a dual wielder.