This guy really should have been called "Security Consultant" or "Locksmith" or something because he is far better with Lockpicks, Damning Testimony, or a Thieves' Kit than with weapons, generally.
Even with investigation tools, though, he is clunky as heck and suffers greatly from the fact that Leo De Luca, Delilah O'Rourke / Lola Santiago, and Hired Muscle / Treasure Hunter exist.
Theoretically Trigger Man offers a nice combo package of three benefits: he cheats an asset into play, he gives you bonus actions (that ignore attacks of opportunity), and he may give you a skill boost. Unfortunately, there are a few snags that end up making him less than the sum of his parts.
First, you have to wait on playing him until you have the desired asset in hand. He looks like a setup/efficiency/action-economy card, but punishes you for playing efficiently and getting value down on the table. If you play Leo De Luca and then .45 Thompson as your first two actions, you'll have only two actions left to shoot with. If you play Trigger Man instead, you get the Thompson out at the same time and can shoot three times right away : twice with normal actions and once with Trigger man. But, if you draw Leo De Luca before your gun you can play him immediately and collect an extra action per turn while you wait for the gun to show up and you'll still be on action-parity with the Trigger Man player when it finally does. Also, trigger Man's own base resource cost is a large as any illicit card's bar a couple of guns, and then you spend resources on the activations too, so although Leo De Luca + .45 Thompson takes more upfront resources to deploy it works out to be comparably resource efficient in the end.
If your collection is thin, you might run him alongside Leo or when Leo's uniqueness is a problem, or just for a change of pace. But Rogue has lots of ways to turn money and XP into actions and I feel that Haste, Ace in the Hole, Honed Instinct, Swift Reflexes and the like just do it better. Several rogue guns even grant bonus actions when upgraded, such as the .41 Derringer and .25 Automatic.
Thus, I think this guy only really makes sense when you get some value replacing your base skill with 4, which is a rough place to be because you can only use him once per turn. And you probably want whatever you plan to equip him with to be something that you could conceivably use for yourself if you draw it without him. The Rogues that consider toting guns already tend to have 3+ strength, and the 2 strength rogues usually plan to fight in other ways and or not at all, and are unlikely to have the stat boosts or icons to succeed even from a base 4. So this is usually going to be a +1 once per turn, maybe sometimes a +2.
The other problem with giving the Trigger Man a gun is that when you need a weapon you usually want to use it several times in the same round to put enemies away, so you may not want to rely on his strength after all. The Trigger Man also runs out of usefulness when his gun runs out of bullets, and while you can reload it with events you cannot play him a fresh gun from hand.
The ideal use case for Trigger Man, then would be to load him up with an asset that can only be used once per turn anyway (because it exhausts), that tests a stat tend to be weak on (will or investigation), for which they can easily stack bonuses, and perhaps one which would normally provoke AoOs.
Lockpicks fits the bill perfectly. You can only use it once per round in the first place, but with Trigger Man you can do it every turn even when engaged without spending your real actions. You still add your agility, so Kymani or Winifred can get the trigger man investigating at a base 9, and most other rogues on base 8, before any bonus from tarot, footwear, other allies, and so on. Charlie Kane unfortunately gains little from adding his base 1 agility unless he has passive boosts on that too, and may therefore prefer a single-stat cluever item that gives some additional rewards such as Thieves' Kit, Damning Testimony, or Fake Credentials.
It's still not great compared to just playing Lola, who soaks more and brings most rogues up to 8+ on lockpick tests by herself while providing a different way to turn resources into clues. But "worse than Lola and Delilah" is unfortunately where most reasonable ally designs are fated to end up.
