So, I have had no luck finding anyone who says the NKE device is really good. Including the dealer. It does look like it fits my paddlewheel socket, which is good. But at NZ$2000 and no confirmation as to whether it can be calibrated, it's a bit on the rich side for me.
Having said that, the Airmar UST800 is NZ$3000 (and definitely needs a haulout to install), so the NKE is the "cheap" option.
Or.... I stick with paddlewheels...
Definitely a market opportunity out there for someone to do it properly and at a believable price
. I note that NASA have been advertising an Electromagnetic version for a while, really cheap
. However, it's still not available a year later (not the only company to have done this). And it's electromagnetic. I understand that the NKE electromagnetic one is useless, and the ultrasonic one is the only option.