Line source loudspeakers are well known in professional audio: they give a good horizontal spread have a narrower vertical pattern. The Pearl linear microphone capsule has similar properties, though these are not its only advantage.
In practice, the ELM series is ideal when you want to record a wide field of sound but keep resonances from floor and ceiling to a minimum. Or alternatively, you can turn the microphone 90 degrees and cut out a vertical portion of sound, e.g. recording one musician but not the surrounding ones.
Pearl ELM-B can be used MS stereo setup (in conjunction with a cardioid microphone) or when used in a pair to create a Blumlein stereo set up.