One of the best 'Hero Ability on an Upgrade' type cards in the game.
You need to appreciate just how absurdly powerful Secret Agent is. It is a better hero ability on a card. Remember, a point of threat removal > a point of damage, generally speaking. Not even taking into consideration that the removed threat is added to the suit form upgrade which can then generate even moar value.
Put it another way. If you can trigger 2 PREPARATION cards in a round - very much achievable especially with Practiced Plan - it is basically the same as generating a 'free' thwart activation with Maria Hill. Except even better because you can split the 2 points of threat removal on 2 schemes.
What makes Secret Agent even better is that you don't need to hard mulligan for it - Fury has other higher priority cards to get into play like Fury's Flying Car and Fury's Watch. In fact, drawing Secret Agent in your opening hand might not be the best. The ideal playstyle is to set-up a bunch of PREPARATION cards and have them sit there until you play Secret Agent, and then you start firing off each of your PREPARATION cards for immense value.
I have heard people saying Secret Agent isn't that good, but people need to wake up and start leaning into this card more, because it is insanely good. By mid to late game, I don't even need to thwart anymore and I typically play Aggression.