I bought this around three or four years ago, when I had my home studio set up in a tiny room with tiled floors, wall-to-wall mirror closet doors on one side and french patio doors on the other.
This thing does what they say it does, so you can’t complain, but it is NOT a one-stop solution for vocal recordings. It will eliminate much (not all) of the room sound, but only with moderate levels. It is defeated as soon as a vocalist belts out.
I spent $299 on it, and in the end I feel it hasn’t quite been worth it. I moved house and now have a decent amount of acoustic treatment in my home studio; in this situation the Reflexion Filter adds little value.
Another gripe I have is its weight: my boom stand got bent at the hinge because of it. In addition, the weight requires you to really screw the clamp on tight, which damaged the rubber grip:
In conclusion, I’d say that if you have no alternative, this thing can help take quite a bit of room out of your signal. But it is no silver bullet, and I question the wisdom of forking out $299 for this. Perhaps that money is better spent on room treatment.