First of all these are flat down to 300hz with useful extension below this. From the point of view of voice reproduction this makes all the difference vs the speakers that only go down to 1kHz. Then, compared to lots of other drivers of this type, are essentially flat all the way to 10kHz. That peak in the top octave is quite beneficial too. Most applications would have you listening to these off-axis and the peak will help to provide some sparkle up there when doing so.
Measuring distortion with this type of driver has to be done differently. Tiny full range drivers aren't designed, in any way, to produce high SPLs. They are designed to cover as much of the audible spectrum as possible but at low to average listening levels. Usually this isn't much of a problem because, while they can't go that loud, you're usually in the nearfield too, sitting 30-50cm away from them.
Still I figured these would be alright being fed 2.83Vrms but, alas, they could not and the shallow profile made them reach their limits. Xmax might be listed as only 0.4mm one way but their Xmech isn't much beyond that. Turning things down they managed to make it through a 100-20kHz sweep at 1.9Vrms.