The ZZ attachments are dependent on the needle bar stroke for the wideness of their zigs and zags. Example, I have both Greist and Singer ZZ attachments, if I put them on a Singer such as the 201 or 15-91 I get a nice wide zz or patterns if you have the one with cams.
However if I try to use it on a 15 clone, it doesn't make patterns worth a hoot and the ZZs are very narrow. Turns out the clones, at least the ones I've got, have a shorter needle bar stroke than the Singers, so they just don't work as good.
Use a ZZ machine and your project will come out much nicer.
Joe