I've got 16 of these things in my studio (4x in each corner of the room, running basically from floor to ceiling). They make a huge difference that is not purely psychological (which, as we all know, can be the case with other forms of acoustic treatment). Once mounted, the room sounded much nicer and had that "quiet calm" you get when walking into a properly treated studio.
I also did some before/after acoustic measurements using a 360 measurement microphone and Room EQ Wizard. The bass traps clearly show a huge difference in the mid/low range. For some problematic frequencies (for example, 40Hz and 50Hz in my room), there was a decrease of nearly 15-20dB. Other frequencies were not as extreme, but as noted, there is clearly an audible difference.
On top of that, they look great! I appreciate the wood panels to add a bit of color, so that my studio doesn't look like Darth Vader's bedroom.