A couple of months ago I changed from the Kanzawa curved to the Kanzawa straight blades. Straight blades are especially good with you need to take off mature coconuts one by one. The curved blade sometimes cuts the stem of a coconut you can't see, then oops, the unexpected nut drops.
They are a little slower cutting than the curved, but they can get in and make a cut in tighter places.
At this point I don't think I'll go back to curved, especially since I have only 1 curved replacement blade, which I am keeping for the pole saw, and 5 of the straight replacements.