FFS uses ultrahigh frequency sound waves (like all sonar), it just has a faster (continuous full screen) update.
Metal (hard surfaces) reflects sound better than soft surfaces, but if the metal is buried within the plastic, its effects should be greatly (if not completely) diminished, so I'm guessing there is something else making the difference in signatures... maybe it's the composition of the plastic itself (which seems unlikely) or maybe it could be some harder finish such as paint on the surface of the bait, or (far more likely) it is the illusive nature of video editing to highlight the one and subdue the other as a gimmick to sell more of these high priced baits.
Basically, I hold the same thought process of Lamar (and Tom) where the difference should be negligible.