Yes, agreed. I had used the link in my post as an example because I had it bookmarked along with other sites to get documents, as well as the official site - wish I would have scrolled down farther on my list instead of using the one I did when I typed that post- it IS a 3rd party site, and although used by some and it does work as @DandyDon has used it, it is a 3rd party site. I had only considered using the official govt site when I went to Coz this last time, but didn't even want to put my info there! Will use the site @cvchief shared (linked below) for Cabo trip, but knowing me, if it doesn't come out looking like the paper copies, I'll probably also fill in the copies I have.
Instituto Nacional de Migración - Forma Migratoria Múltiple
www.inm.gob.mx
The question is WHO is collecting your data on a 3rd party even if they are not charging? It is the goodness of their hearts?
oh and print the FMM double sided. it looks like crap as it doesnt line up, but immigration is used to it and doesn't care. At least in CZM. I haven't brought a tourist through CUN in a while.