Thanks! I appreciate the opinions that they should be trustworthy with the checked bags. I would be flying out MEX-JFK and currently it seems I would pick a regular carrier like AeroMexico or Delta for that, so I won't have to deal with the Guadalajara staff!

If I do the "Extra" fare it should give me carry-on in addition to personal item so I can remove my computer from my backpack before checking rather than leave valuables in there, but if they are no issues with honoring the add-ons, then I would definitely prefer to just have the whole backpack with me (the 15kg carry-on purchase). Weight-wise I'm usually at 10-11kg, will just need to compress the size as much as possible in case they try to check! This may be a rare case where I have to pre-pack as a test before I can buy the ticket, ugh.