Hi George, I'm a bit skeptical here as well.
The only thing I object to is "doublestack performance" if they just mean 0.3-0.5 Lorentzian bandpass. That's very good, but not doublestack. You'll still get parasitic continuum light. Depends on the profile of the bandpass. Unless this really is something new.
It is interesting that the description states 'double stack' with single quotation marks. Interesting that is sells for ~ $700, while the standard 60 mm scope with a regular Quark is ~ $1300, (80 mm is $2,700), and a Quark prom/chromo/combo by itself is ~ $1200. I would have to believe something has to give for it to be sold for only ~ $700.
What has been happening "industry wide" is that to increase market penetration and increase sales volume, quality standards for contrast uniformity and finesse have been loosened for entry level and consumer grade H alpha filters so they can be mass-produced for relatively low cost. DayStar has done this with the Quark. On the other hand, SE and PE filters have remained at about what they cost when first introduced in the mid-late 1970's - adjusted for inflation of course.
Until someone can actually get one to review and perhaps see what's inside, my best guess is that the 'double stack' is not a second etalon, but a narrow-band filter of about 1 to 2 or more angstroms FWHM, tilt-tuned (via the stainless knob at the front red anodized element) and is followed by a Quark version that is temperature controlled like the standard Quark. It's also difficult to understand what "great strides in cost reduction" have been made which allow an already entry level filter system to be further reduced in price while adding a 'doublestack' and ancillary optics, carbon fiber tube, etc.
I would note that a 1 - 2+ angstrom coated filter of decent quality would cost a few hundred dollars by itself (Andover 5 A 12.5 mm diameter is $625 https://www.andoverc...ndpass-filters/ ), let alone adding the optics, mechanics, and the Quark (?) filter element, which would still appear to need the telecentric lens system.
It remains the bane of the industry that they haven't developed a standardized set of parameters for evaluating and communicating filter quality other than almost meaningless FWHM specifications. Until then it's buyer beware, and high quality usually always cost more.