I have significant experience with the Raidho D1.1 and a bit less listening experience with other D series models. So, in a "very short period of time", Borresen with the M1 came up with an extravagant variation of the D1.1 design (with even stiffer??...zirconium sandwiched 4.5 inch drivers (with includes pockets of zirconium powder and other 'magic dust'?), that still allows the design to only go down to 40kz). Many would suggest the acoustical laws of physics are at work.
GIMMICKY DESIGN VARIATION is the key criticism I have. I do believe the M1 is more expensive to manufacture, and that theoretically, the materials/design changes result in 'measurable' sonic improvements, and maybe even a subjective degree of real world listening improvements. However, I casually see the price differential between the M1 and the D1.1, akin to installing 24 karat gold knobs and switches on your pre-amp. Mike Borresen impressed the audio community with his design of the Raidho D series. But I have to wonder how much sonic improvement the buyer actually gets out of spending an additional $70k for a 2-way monitor, which is in many ways a glorified monstrosity of the use of expensive materials and design concepts. Or am I wrong and Borresen has redefined the laws of physics?