I wonder why they chose to tell the users when they registered, instead of waiting? Could they have gone ahead and let them place orders for DDOS attacks, to capture more proof of the users' criminal intent, or would that count as entrapment? Someone who 'merely' registered could try to claim that they were a researcher, but if you hit the button to DDoS someone, that's going to be more difficult to deny responsibility for.
[Edit: Now that's making me imagine a disgruntled user suing the NCA for breach of contract: "I paid money for a DDoS and they didn't provide the service!"]