Is an instruction to the jury that the jury should accept the testimony of an undercover agent prejudicial?

All parties claim that the district court committed reversible error by giving an undercover agent instruction to the jury similar to the one given in United States v. North, 746 F. 2d 627, 631 (9th Cir. 1984). They contend that the North instructions apply when there is a claim of entrapment and since there was no claim of entrapment in their case, the instructions gave the government's use of the undercover agent a sense of legitimacy and contradicted a companion set of instructions warning the jury to accept the testimony of the informant with caution. For these reasons, the parties assert that the undercover agent instruction was prejudicial.