HFT High Frequency Transducer

Is any body experiment with these tweek, that treat the listening room ?  5 of these would supposed to give an improvement.  Do we have to continue to 15 or 20 ?  Because they are not cheap !
I use the Synergistic Research HFT's in my listening rooms. This is after trying to go the more traditional way of improving room acoustics with GIK acoustic products.

For me the advantages of the HFT approach is: easier to install and to dial in the optimum location of the devices, they are not visually distracting, and if you move you can easily take them with you.

Since they come with a 30 day trial, I think many audiophile rooms would benefit with an audition. and if you do not like them the cost to return them is under ten dollars. It is a fun and educational  weekend experiment.
David Pritchard
folkfreak.  But you could make your own :-) ...
What is the recepe ?  Is it easy to make ?