Honestly? The big battery does last longer. Never knew why before.
Batteries are...eh...fickle. You might see that there's a protection circuit board that the leads are soldered to on all of these: this disconnects the battery once it reaches a certain low voltage state in order to prevent over-discharge.
Most common issue with these is that they end up in a drawer when they're dead, then someone goes to change em up...suddenly the battery can't hold much of a charge any more. You can't drain these until they're flat: they *really* don't like that.
I wonder if some of those reviewers may have treated theirs badly, or perhaps they were simply held in storage for too long and not sufficiently pre-charged.