Correction - I was just at Klingspors. and they are $160 and $280 for the two sizesCommercial Longworth chucks are available, as I recall handling them at some Klingspors show a few years ago. They weren't inexpensive ($85-150 IIRC???) for various sizes, and while I thought those were reasonably well made, I chose to spend my $$ elsewhere. I may still purchase some day.
I've got the commercial one and it does work, you have to be low RPM and very gentle. I've lost some bowls and I would not recommend it. Jam chuck is the way to go!I was really asking about the commercial ones that are available through the woodworking sites. The ones at Rockler, for instance, have really good reviews.