Half Elf Bard Substitution Levels

[G.Cube]

Why are they considered good? I don't really see it. If someone would, could I get a quick explanation for all three levels?

[Telonius]

The first substitution is the best. Soothing Voice replaces Countersong, which is a (typically) lesser-used ability. It's much easier to get a higher skill check than it is to increase the save DC of a spell normally, and Diplomacy is an easily-pumped skill check. As a Half-Elf, you get a minor bonus on it; as a Bard, it's on your class skill list (along with all of the synergy skills to help it). Against an enemy, compare the Will save of this ability to the Will save against a regular Calm Emotions spell. Yeah.

The ability itself is pretty versatile. It can stop a Barbarian rage, eliminate any Morale buffs the enemy might have, or remove a Fear or Confusion effect from an ally.

For Command, it's a spell and effect that Bard doesn't usually have access to. The order you issue doesn't have to be particularly reasonable, either, unlike Suggestion. On the other hand, the save is easier than Suggestion. (11+cha instead of 10+1/2 Bard Level+Cha). Personally I wouldn't take this, but it might have its uses.

Secrets of the Diplomat - Adds to Spells Known, from lists that you normally wouldn't have access to. Versatility is good, and it's not like the Bard is overflowing with Spells Known. The catch is that your 4th-level spell is chosen for you - and 4th level has quite a few very, very nice ones, like Greater Invisibility, Freedom of Movement, Legend Lore, Modify Memory, Hold Monster... Personally I find that Sending is best in Scroll form, for those few occasions that you really need to contact somebody half a world away.