Another enemy signature weakness. Looking at the two elements, the effect and the discard condition, we get:

The effect: Easy to hit, hard to damage, hard for Nathaniel to Evade, hits pretty hard. Normally, this is 3 actions to clear, although you can speed things up with Beat Cop, Counterpunch, or Survival Knife (probably with Bandolier). Guard Dog can also help. Handcuffs shenanigans are also a possibility. This card will pretty much cost you a turn, one way or another, but is rarely a danger to either the scenario or campaign.

The discard condition: Kill Tommy or put the cuffs on him; your choice.

All in all, this is an average signature weakness.

Why should you take Handcuffs just to handle Tommy? From a naive action-cost perspective it doesn't seem to make sense: you just spent 2 resources, a card, and an action to save yourself 2 actions, in a class that isn't known for having an excess of resources. Effectively you're playing a Swift Reflexes, which isn't even a particularly good card on Rogues, much less Guardians.

But there are three important reasons why you would do this. Firstly, Cho will almost certainly draw through his deck every scenario, meaning that there's a good chance of seeing Tommy twice if not for Handcuffs. Secondly, you only need to pass a single test, not 3, which is particularly important at higher difficulties. Thirdly, it means you can draw safely during your turn. Since it usually will takes 3 actions to clear Tommy (baring Beat Cop (2), Dogs, and One-Two Punch), it'll feel terrible taking a draw action and find Tommy while trying to refill your hand. Banking an action with Handcuffs will save you from being smacked around by Tommy for a turn, or deal with him easily if he's drawn by an Overpower or Glory.

If we consider a weakness' strength based on how many actions it takes to get rid of, Tommy Malloy is pretty harsh. His ability basically requires your team to spend three actions, minimum, to off him, which is more than most weaknesses.

There's also very few ways to mitigate the action sink, especially at level 0: you can use one-two punch to get 2 damage in one action, but you just played an event that normally does 4 damage for 2. The other option is Beat Cop, who you'd rather keep around as long as possible. Combine both and you can do it in one action, but you just spent six resources, static +1 combat, some soak and your most damaging event to remove a weakness. I'd rather just blow a whole turn taking basic fight actions, since Tommy's crummy fight stat makes him easy to hit.

In multiplayer someone could evade him, but solo that's really not an option. Even then, someone has to deal with him eventually, eating up your team's actions.

In short, he's really annoying, and will probably take three or more actions to get rid of. At least you can play Glory when you kill him.