I have installed the UltraSonic system on M/Y Saba, a 16.5 meter steel trawler about 3 years ago.
The unit I used is 1 sounder in the forward part of the yacht and a double unit with 2 transducers placed right above the props. We used a 220 & 24 A/C & DC system.
Over time my over all experience is that it really works. We have recorded almost zero barnacle and algae growth. My yacht is covered with International Antifouling and this year when lifting her out for the annual maintenance we concluded that there was no need to paint. This amounts to savings in fuel and paint/dry dock cost.
Currant draw is minimal and system is left on at all times.
I do recommend installing it.
Keep in mind that the system will not work on glass (underwater lights) and stainless steel.
Enclosed are 2 pictures of her bottom and keel prior to an anti fouling coat and one year in the water.
Regards, Yuval Haft.