Is there any difference between an informer's privilege and the observation post privilege?

While it is clear that the policy considerations which support the informer's privilege are essentially the same as those which support the observation post privilege, there is a significant distinction between the two situations. That distinction was concisely stated in one of the most fully considered of the many American authorities to which we were referred: An informer's participation usually ends with the communication of the "tip" to the police. Most often, the informer has no further involvement in the activities that lead to a defendant's arrest. However, a police officer seeking to assert a surveillance-location privilege may often be the crucial, and perhaps the only, witness to the criminal transaction. (State v. Garcia, 618 A.2d 326 (N.J. 1993) per Clifford J. for the court at p. 331)