Good pull, mykyll2727. The third pic down shows D. Graebener - formerly the G in BG - with the president of HiVi/Swan. Obviously Swan have done a lot with linesources and line arrays, all including some version of planar-magnetic technology. I prefer it in treble drivers, but it can be interesting in nearly any length. There are twin six hundred foot continuous arrays of the six foot BG planars in the German Parliament engineered and installed by some close friends of TAI.
The original push-pull technology, IIRC, was an implementation by Strathearn
of Scotland which was eventually sold to a German firm, I believe (I've seen the original tooling, and its owners now build their own version of this type of driver on new production apparatus). Gold Ribbon Concepts
developed an American version based in Iowa in the eighties, and the Carver Amazing Loudspeaker used Graebener's version, built by him in Washington State. BG in Nevada was founded in the mid nineties and continues to the present day with drivers from a few inches to six feet long.
A raft of smaller treble units, all based on the now-familiar multiple rows of magnets - first ceramic and now commonly Neodymium - are made by a variety of outfits. We use some in our products.
Very wide band planars (physically long drivers) operate predominately as linesources, with certain fundamental differences from point sources. Among them are less attenuation over distance, a directive propagation toward a listener within the ends of the line, and a different impulse behavior - they're basically two-dimensional radiators, having no third or vertical dimension to their dispersion when the wavelengths are small compared to the length of the line. Flat amplitude responses can be challenging over more than a few octaves, and it's not uncommon to see these big drivers equalized and/or used as midranges as an essential part of the design. Alternately you can use line arrays of discrete tweeters and midranges in big multiways. They're come a long ways.
They have their fans, which owes to the sense of resolution a large, "fast", wide-dispersion single driver typically exhibits. Used in large systems and within multi-way arrays, they can build a room-filling sense of soundstage without the "push" and strain of some smaller multiway point sources. They say there's nothing like sheer cubic inches, and by the time you support the big line with treble and bass (and occasionally midbass) you'll have a very large (and expensive) system.
TAI works with planar lines, including in public venues. I'm currently engineering a three-channel setup using a pair of 12' lines plus center monitor for a five hundred seat performing arts theater and music performance venue in SW Florida. Used in these lengths there's nothing like them to saturate the furthest rows of the audience without causing the first rows the usual pain of a "loud" output. This has also been a common setup in Europe.