He's not that great... at least for now. But there are some uses most people tend to not think of:
- His ability can be used to shuffle your library like Myr Mindservant. Minor function, but it can have some use.
- Artificial Evolution can be used to change "Mercenary" into any other type you like.
This can turn Cateran Persuader into a useful, cheap one-drop fetcher.
Human and Goblin are two good choices for example.
Sneak in a Magus of the Vineyard during your opponent's turn and use the mana.
Sylvan Safekeeper and Weathered Wayfarer make a nice team as well. It unfortunately relies heavily on Artificial Evolution, so it's too risky in general.
You could also use Conspiracy, but there are plenty of other more effective combos for that. But Cateran Persuader might still make a good one-of in a Conspiracy-centered deck.