About 25 years ago, JW Fishers lost interest in PI's, they had engineering expertise in sidescan sonar and plowed that field instead. Easy choice to make.
About that same time, White's got interested in PI and came out with the red thing in the cylindrical housing, I forget what they called it. Between the White's and the JW Fishers, it was an easy choice. The JW Fishers was a bit "hotter", but almost unusable, whereas the White's was a very well thought out product.
Several years later I had to race the protype Fisher Research Lab (not JW Fishers!) Impulse against the newfangled White's autotune and differently packaged PI. In the wet salt. The Impulse had problems, but the newfangled Whites' was completely unusuable due to the "autotune". It stanked in the surf.
Fisher no longer makes the Impulse. Even though it was my baby I have no desire to bring it back, the CZ-21 is a vastly superior non-PI product. Meanwhile, nothing I've heard regarding White's beach & scuba PI's these days makes me think they're superior to that first White's PI. And the JW Fisher PI's? Back in the stone age they were relevant, that was then and this is now. In saying so, I'm not grinding a personal axe against JW Fisher, I've always respected them. I'm just reporting a bit of metal detector history that explains how we got to where we're at now.
--Dave J.