Dunlavyaudio.com has an article called "cones, domes and planars" underneath the tech talk icon. Its a little more technical than the sequarra one (I just read the sequarra one. I didn't know about it , thanks for the link), but more general. And it gives a good oversight, although biased in its own right. There's five different ways to produce sound in high fidelity: electrostatic, electrodynamic, ribbon, bending wave transducers, and plasma drivers. Alot of it depends on how well its done (although the last two a pretty "high-end" at any level). The planar technologies are the only two suitable for the line array design (electrodynamics run into too much interference among the drivers), although I believe Nelson Pass' "ion cloud" from the '70's was a plasma driver in some type of "electrostatic" design, so its dispersion characteristics may have pushed it out of the point source class, I'm not sure. But its healthy to look at it from both sides like your trying to do. Some ribbons can be pretty bad: like the Monsoon speakers on your PC versus some Raven R3's. VMPS' site wasn't working when I tried; I don't know what ribbons they use (Bohlendar Graebener's maybe, I doubt Newforms, but I don't know) but with a 7" length you won't have much vertical dispersion, which is good and bad. It minimizes ceiling/floor reflections, but the overall vertical polar response may be a little weird (I don't know where the crossover points were and what not.) Ideally an audition, but at least VMPS doesn't look like they are skimping on parts cost or anything (like Genesis using $200 Carver ribbons in a $70k+ speaker.) But the "old-fashioned" cone driver can still be state-of-the-art when done right. Not all cones are equal and not all ribbons are equal. Dunlavy shed's good light on the efficiency aspects of planars v. cones/domes.
