Yeah, here is his response when I asked them about why they switched their recommendation:
Ken said:
We know, we know! We've been recommending Denso Iridiums in the past. They worked great for us for very high hp applications (650+rwhp), so yes, we recommended them.
Recently, a few customers using them for high hp applications reported back to us they experienced early failures with this plug, and substitued another brand with longer lasting results. This does not mean Densos are bad; they are not. It would only be fair for the customers to take this up with Denso and let them determine if any issues exist.
Often, we get dragged into situations we do not want to be in when "recommending" another product other than Kenne Bell. This is the case with Denso. Any issues with plugs should be taken up with Denso, not Kenne Bell.
We still fully support Denso. Denso makes another very good plug called a "U-Groove", and when gapped at .025" with our supercharger, they have been working well, and time will tell if they hold up better in ultra high hp applications.
A lot of the high hp guys have switched over to an NGK TR6 plug with success. Take it for what it's worth. We are just passing along information we have received from other customers.
Yeah, from my talk with Ken he basically said that KB recommends the Denso U-groove now. If you can't get the U-groove, then get the NGK TR6. But he made it clear that their first choice was still the Denso. I guess you can't go wrong with either though.
Sell them in groups of 4 to the billions of ricers that don't know what they're doing and will buy anything that someone tells them is the thing to have for more power.