I'd like to take a shot at your question, with a bit more emphasis on the mechanics of why the Sound Labs might be preferred to the Martin Logans. Let me state up front that I'm a Sound Lab owner and dealer, but I'm not going to go into a subjective comparison here.
But before I get started, let me point out that Martin Logans go through quite a bit of change and improvement as they break in - I'd say moreso than the Sound Labs do. On the other hand, a pair of Sound Labs that hasn't been plugged in and charged up for at least five days isn't going to sound its best. So to anyone making the comparison, make sure the Martin Logans are fully broken in and the Sound Labs are fully charged up.
Sound Lab speakers have some unique characteristics which might contribute to a subjective preference:
Sound Labs use the thinnest diaphragm in the industry - last time I checked, 1/20th the thickness of the diaphragm the Martin Logans use, and about 1/5th the thickness of the nearest competitor I could find. In theory, a lighter and thinner diaphragm should be more articulate, all other things being equal.
Sound Labs are probably the only truly full-range electrostats, if you take full-range to imply response below 30 Hz. A full range electrostat avoids many of the compromises of a hybrid, for it is difficult to do a good job of integrating tall, line source dipole panels with monopole point-source woofers. I must admit that Martin Logan has done a very good job with their new dual-woofer hybrids. I think what they are doing is using the two woofers as a dipole (out of phase) in the crossover region, then they have an all-pass filter on the rear woofer to bring it in phase at very low frequencies, to give you the very deep bass. But the problems of integrating woofer and panel go beyond the problems of integrating dipole with monopole - you also have to integrate line source with point source (which means the tonal balance is distance-dependent). A full range electrostat doesn't have to take driver integration into consideration and juggle all these parameters.
In my opinion, one thing that really distinguishes the Sound Labs is their unique radiation pattern, which generates a reverberant field having the same tonal balance as the direct sound. Like all dipoles, the Sound Labs have a figure-8 radiation pattern in the bass. But then as the panels become directional their faceted-curved geometry radiates over a 90-degree arc front and back, maintaining that same figure-8 radiation pattern all the way up the frequency range. So the energy going into the reverberant field has the same tonal balance as the on-axis energy. Research published in the Journal of the Audio Engineering Society documents a correlation between listener preference and a reverberant field that sounds like the direct sound. This is because the ears derive timbre not only from the direct sound, but also from the reverberant sound. Note that a reverberant field with the same tonal balance as the first-arrival sound is a characteristic of live, unamplified music, but very few loudspeakers mimic this because their directional characteristics change with frequency.
I'd like to take a closer look at a characteristic mentioned earlier, and that is the Sound Labs' line-source radiation properties. Sound pressure level falls off linearly with distance from a line source, and with the square of distance from a point source. In a normal listening room the reverberant sound fills this in somewhat, but a few numbers might be interesting. Using pink noise, I measured a point source loudspeaker at 1 meter, and then back at 8 meters. At 8 meters, the sound pressure level had fallen off by 11 dB. Then I repeated the measurements with the line-source Sound Labs. The sound pressure level had only fallen off by 4 dB back at 8 meters! Once again, this more closely mimics the sound field of a live musical event, where the sound pressure level doesn't change significantly as you move around the room.
As long as you are shorter than the panel height, you can stand up and the tonal balance remains virtually unchanged, and the wide, consistent radiation pattern means the tonal balance is the same throughout the room. Since I like to dance around when no one is watching, I especially like this characteristic of the Sound Labs.
I would say the Martin Logan Prodigy's are the most advanced example of hybrid electrostatic technology to date (not counting the 80-grand Martin Logan Statements). The big Sound Labs might likewise be considered the ultimate development of full-range electrostatic technology. Both approaches entail compromises, yet both are (in my opinion) significantly more convincing than competing box loudspeakers.