'Tyfon' seems to be the cultivar name, and "Holland Greens" seems to be the common name, so far as any new crop has a common name. Maybe it should be "also sold as Holland Greens".
You can see descriptions at these vendors with these item numbers:
Nichols VGR472
Pinetree W336
Here's an enthusiastic blogger who says the cold-hardiest green he's found.
Ben also says that it doesn't mind heavy clay soil:
http://blueboathome.com/blogs/...
Holland Greens (Brassica rapa 'Tyfon')