I'm pretty sure I have the Natsudaidai orange/pomelo and also grow the New Zealand lemon. They are two different tastes. The NZ lemon tastes like a sweeter lemon while the Natsudaidai does not taste like a lemon to me at all.
Natsudaidai is more of a grapefruit/orange taste to me. Not as sweet as an orange. Fruit is smaller than an orange, and flat, skin color is dark yellow. I had my tree for years, from my father who grafted it for me over 40 yrs ago.
The Sanbokan tastes similar to the New Zealand lemon but it is much larger fruit and looks like a sumo with the bump/neck. I can eat the Sanbokan out of hand and it is not too acidic like a lemon so it is good tasting. Natsudaidai is sweeter than both fruits on my trees.
Is anyone else growing the Natsudaidai?