Anyone used Scan-Speak's "Flow Resistors" or "Aperiodic Vents"?

Yes, I have used them in three projects with nice result.
You can reduce the size of the box a little bit, like 20-25% and still have the same performance but you can't half the volume or something like that.

The best thing they do however is to lower the resonance peak, which gives a over-all better bass.
In 3-way design this also make crossover design easier.

The best results I have got have been with drivers that have a Qts around 0,45-0,5, and a Rf/Qes ratio of 50-60.

Janne