I have been using the HFT with significant improvements of my room acoustics. I purchased 2 boxes (5/box) and installed these devices as per SR instructions. Basically, it has transformed the acoustics of my dedicated audio room. Their acoustic effect is like getting rid of all walls in the room, minimizing room reflections. Soundstage increases dramatically in depth and width. You will hear additional micro-details from well known music tracks, etc.
Was very sceptical prior their purchase, since they look so minimalistic and innofensive. I tried their 30 days money-back guarantee offer and after 5 minutes of listening, I was sold. Same results with their FEQ device, this little box will lock the bass like an anchor. Overall, one of the best tweaks I ever purchased. Also saved a ton of money, not buying the large acoustic panels offered by acoustic engineering firms. As a bonus, WAF is 10/10 for these little 'cones' :-)