It’s not a dumb question at all. The biggest difference is in the printing style. Zaner Bloser is straight up and down writing, sometimes referred to as “stick and ball.” D’Nealian printing has a slight slant and teaches the children to put little curves at the end of their letters, in preparation for joining those curves when they transition to cursive.
If you download the sample of Delightful Handwriting, you’ll see the variation in the printing. The cursive is a little more similar— still some difference between a few letters’ formation and Zaner Bloser has more of a slant—but cursive is pretty much cursive.
Does that help any? Don’t stress too much about which one to use. The main thing is to help your child write legibly. 