I can see how interfaces benefit from an in-person demo, but even with those types of modules, actually hearing the A-198 being used to play some music with lots of portamento and tremolo in a sound clip does help to show off what it can do that you can't easily do with, say, a MIDI keyboard, even with pitch bend.

Certainly in the case of sound generators such as oscillators, noise, drum modules and so on, and effects such as filters, distortion, delays and so on, it helps even more to hear what it sounds like first.

Just a suggestion, anyway. :)
Zoë.