The term "soundproof" (even as their information states) is misleading. Perhaps better than you'd imagine, but am doubtful.
First there are the inevitable gaps at top, bottom, and ends. Real soundproofing requires air tight seals.
Second is the stated reduction of 50%, that's just 3 dB. The small thumbnails have no links.
Third as stated the curtains provide a degree of sound absorption which can be mistaken for soundproofing (creating a sonic barrier).
Fourth the term "quenching" is not defined as it applies here, the last two links are press releases.
Fifth don't see any reference to STC (sound transmission class) as per ASTM E90 and E413. (Hospitals for instance are required to reduce sound transmission by 35 to 65 dB (depending on the circumstance).
