I completely misinterpreted the text on Robert's ability, so my review is quite misinformed.. I'll leave the original comment as maybe it will prevent someone else from making my mistake.

The ability feels quite different than the upgraded Robert Castaigne

This is also one of two level zero allies for rogue that adds ; the other being Lonnie Ritter

fighters tend to rely on more actions, to defeat enemies as compared to fighters with big damage numbers. This is another card to theoretically save actions.

How many actions do you save to gain what is virtually one more ammo? I suppose this depends on if you are stocking a lot of weapons with low ammo. You don't save as much if your weapons have a lot of ammo already. Keep in mind this ability is only for discarding one handed weapon which are typically lower damage (with one exception detailed later). The other benefit is if you are out of ammo, and haven't evaded the enemy to exhaust them, you might avoid an attack of opportunity if you can kill the enemy.

it's not bad with Dirty Fighting, when you are out of ammo on .41 Derringer maybe you can use that extra action to play the next firearm.

Best use might be one more use of Sawed-Off Shotgun with Well Connected and lots of resources. This can easily become big damage (imagine Jenny pulling her elder sign) Feel free to dabble with Mob Connections to bring it back, but since that is 2 resources to recur and 3 more to play the shotgun, you will need to watch your funds to keep Well Connected providing a good bonus.

With experience it is recommended to upgrade to Robert Castaigne as it has simpler combos and is less resource intensive.

In my opinion, if I have to choose one early ally to add I would favor choosing Lonnie and a Trench Coat or Heavy Furs for damage mitigation and other bonuses. Later I would consider the upgraded Robert Castaigne instead of his zero version.