The rear shouldn't be SBR, it says 18" barrel and the Mech-Tech upper for Glock isn't considered SBR. The forward would definitely be SBR.
I think a single carbine with the magazine forward the pistol grip, utilizing a Beta C-mag, would be a much better product. That thing doesn't look very ergonomic, looks like there might be issues if the barrels aren't EXACTLY lined up, and would likely damage the finish on your weapons. It would make more sense to me to just come out with a double-barrel rifle instead of using this bizarre contraption, or having an upper which replaces the slides and uses two Glock frames as the lowers.