@Silverfang000 I don't recommend it has too many disadvantage.
1, Using Nen isn't just a superpower; it’s a high-stakes trade-off involving the user's life force.
Death or Loss of Power: If Kurapika uses his "Chain Jail" on someone who isn't a member of the Phantom Troupe, the Nen blade around his heart will kill him instantly.
Permanent Physical Damage: When Gon made his vow to defeat Neferpitou, the "rebound" left him in a state worse than death—his body withered and he completely lost the ability to use or even see aura.
2. "Memory Overload" (Capacity Limits)
Hisoka introduces the concept of Memory Overload, which is a strategic disadvantage for Nen users.
The Flaw: If a user tries to learn an ability that is too complex or doesn't match their natural Nen type (e.g., an Enhancer trying to master complex Manipulation), they "clutter" their brain.
The Result: They might lose the ability to use their fundamental skills effectively in the heat of battle. Kastro is the prime example; he focused so much on creating a double (Conjuration/Manipulation) that he forgot the basics of Enhancement, leading to his defeat.