Reinbach comes with a significant advantage when he is recruited - his Red Rose Rune is in the head slot that characters don't unlock until very late game (many will not unlock it at all, and you still need to do extra grinding in Obel to reach the high levels for high SKL fighters to unlock the head rune slot). He can't use Kangacorns like the normal 1-handed swordsmen, but he'll have 2 free rune slots to supplement the Red Rose Rune attacks.
I'm noticing this now in my S Rank playthrough where I am purposely not grinding in order to gain enough EXP in each story/quest battle. I'm pretty late into the game, with characters reaching level 30+. Nobody has a free head rune slot yet, so Reinbach having the Red Rose Rune in the head slot and 2 other free rune slots gives him a pretty big advantage.
Now the Red Rose Rune's 1st skill isn't too impressive, it's a 100% damage attack. His second is an AOE sleep spell that does no damage. But it's pretty much no worse than the Viper Rune for 1-handed sword users, which only has 100% damage attacks as well. The thing about special attacks is they don't miss, so it means you can use Berserker Belt and not have to worry about accuracy issues. The Red Rose Rune's 3rd skill also has a big AOE that deals 80% damage to all enemies (with a high chance of causing sleep to the targets as well) - I believe the AOE is better than the Viper Rune's 3rd spell and matches the Eagle Rune's 3rd spell AOE.
So with the 2 free rune slots and already having access to a no-miss attack, it means Reinbach can use 2 passive effect runes like Warrior and Gale, or once he gets a 3rd spell, I'd opt for a Sword of Rage and Warrior. With the Warrior Rune and magic sword, as well as a way to use level 1 attacks that don't miss, he will hit like a truck. Even using the Red Rose Rune's 3rd spell can 1-shot everything if you augment his attack with Warrior and Berserker Belt - no need for rare S Rank equipment.
As a Noble, Augustine has a somewhat limited set of options for Hand accessories, but he can make up for it by using jewelry (Fancy Necklace and Drop Earrings), and late game you can find some great equipment that nobles can wear (that most males cannot) - Venus Armor, Venus Gloves, Bondage Suit, Bondage Gloves...
skill-wise, Reinbach (and Charlemagne) have a unique skill, Narcissism, that increases damage. Now I don't know if this skill augments ALL of his damage, possibly only regular attacks-- further investigation is needed, but on paper, the Narcissism skill gives him a significant damage boost-- 16% at B and 25% at S.
Reinbach also has the important Extra Move and Godspeed skills.
stat-wise, Reinbach's best stat is Skill, which is so important in this game since it determines a fighter's MP. He will be one of the earlier characters to access a 3rd spell and start causing havoc with the Sword of Magic spell.
Reinbach's also got a high LUK stat growth, so you could possibly build him for critical hits with a Killer Rune, but I'd rather focus on the guaranteed damage with weapon runes.