This is an interesting card, and some ramifications are not quite apparent at first glance.
First : the Illicit asset does not cost any ressource to put into play from your hand (nor any action either), but once it's attached to the Trigger Man, you have to pay 1 ressource per use. Most Illicit guns have a cost that is either the same or higher than the number of ammo it comes with. So a gun with 3 ammo that normally costs 3 ressources to put into play will cost you 3 ressources to fully use with the Trigger Man. With "more expensive" guns like the .45 Thompson, you can actually save a ressource, and in all cases you have the advantage of paying only for the ammo you actually use.
Of course, you have to factor in the (non-negligible) cost of the Trigger Man himself. But you get what you pay for : "fast" actions with a base value of 4. Interesting for a low-Fight rogue who wants to use weapons. The lower your stat, the better value you get from this, so Kymani, Trish and Sefina seem like good candidates. Alternately, a low-Int rogue could use Damning Testimony or, with less benefit, Lockpicks for this. And for our good mayor Charlie Kane and his horrendous stat line, it's even better, for fighting or investigating ! (It would have been awesome for Preston Fairmont, but you can't get any Illicit cards in his deck, so barring any "card-sharing shenanigans" with teammates, it doesn't work.)
Second : Nothing says you can't use the "activate" action on the asset yourself, even once it's attached to Trigger Man. So you could decide to use the gun (that you put into play for free) yourself, without paying the Trigger Man's 1 ressource. Probably not a good strategy by itself just to save money, but could be useful in a pinch, if you need to attack again.
Third : Nothing says the asset stops using slots, so you have to "share hands" with the guy, both of you holding stuff together. Weird, but OK
Which brings me to : other interesting assets that don't use hand slots.
Burglary : For 1 ressource, Investigate as a "fast" action with a base value of 4 to gain 3 ressources. It becomes a money engine, especially if you can boost your investigation with Magnifying Glass (Finn, Kymani, Trish)
Liquid Courage : Heal without spending you precious actions, at the cost of paying more. For rich rogues.
Disguise : Tony Morgan could reliably evade at 6, if necessary.