The Nagler zoom offers the best possible imaging quality and keeps up with the best planetary eyepieces in direct comparison. And compared to the Ortho's it offers four focal lengths, a wider field of view and a much more comfortable viewing experience.
The type 5 eyepieces with 20, 26 and 31 mm are ideal for short focal length Newtonian telescopes, even on the 20" f/4 stars are absolutely point-like almost to the edge.