I think you'll find that cheap wide ange EP's aren't Kellners, they tend to be modified Erfles or modified Konigs.
Kellners have an FOV of only around 45 degrees, about the same as a Plossl.
If you're interested in eyepieces, here's a great read:
http://www.howardastro.org/documents/evolution_of_eyepieces.pdf
Cheers,
Jason.