The D27TG-05-06 is a conventional 1″ fabric dome tweeter with ferro fluid (pictured below on the left).  Resonance is a respectable 1 kHz with a Qts of 0.77, sensitivity is advertised at 92 dB.  Testing is done at -5 dBW (should have done at -2 or -3 dBW).

The frequency response is quite smooth, with a few dB of gradual roll-off on the top end.

What is even more impressive is the distortion performance – this unit is 6 years old, been sitting around in a box!  Distortion is at -50 dB from the fundamental through most of the band above 2 kHz.  The third harmonic only rears its head at 4-5 kHz.  This tweeter could easily cross over at 2 kHz at 2nd order, and maybe 1.8 kHz at 4th order if you wanted to push it.  That explains why this tweeter has had such a long life and is still available.