That's not "control," and is completely false and misleading.  An API key is not the same thing as a private key.  If my funds are locked in your service with the only access I have being an API key, that means that I have no control.  The API key, or the service as a whole could be disabled by you at any time, and I don't see anything that  guarantees you won't do just that once the funds are deposited.

Not to mention that your service smells like a ponzi scam to begin with.