Despite its slightly higher damage and ammo-to-reload ratio, this card is mostly outclassed by the Monkey Investigator, which costs 3 Gold instead of 4 and has a useful On Play effect, and Mine Supervisor costing 4 Gold but consistent DPT and is a Rare with additional utility. Crossbow Monkey's only benefit is more burst damage and is affected by the Super Monkey Fan Club.
Crossbow Monkey does one-shot Red Bloons outside of Dark Castle, unlike Monkey Investigator outside of Game Night.
On a deck that relies on Fan Club synergy to defend, the Crossbow is worth bringing if combined in a deck with a mid-game wincon, to defend for a while before the final kill, particularly for OTK decks.