Now that's quite an awesome action pose there ^^
Die cast parts for the waist joint.
Comparison with G.F.F. Vol. 0030.
Apart from the differences in the color scheme and marking design, G.F.F.N. Z II has die cast parts to increase the strength of its joints and the stability for its transformation. You can say it's a different design for the same MS, with an increase of 3,200 Yen in terms of its cost ^^;
All images from Moeyo and G.F.F. Maniax.