"If the manager thinks that the findings are biased, would it be better not to say that, or communicate it in some other way?"

Describe the points of the analysis that seem biased, without even using the word "biased".

"Looks like you only considered..."

"I don't see any mention of..."

"But you didn't mention [superior feature] of [other product]."

"Biased" is an accusation against the presenter, as opposed to asking questions or making comments about the analysis directly. Making a personal attack does not help in making a good decision.