I did it about 5 years back. My main point of entry was MEX. Overall I found the program to be worthless, and let it expire.
Issues - they had two VC machines. More often than not they were out of service. The actual process was not very different than filling out the old form, just doing it on a screen instead of paper, so little time savings. Lastly, the printed "visa" was treated with suspicion every time from both airline reps at departure check in, to the visa collection when boarding (though with paper visas no longer being the norm this is less of an issue.

That being said, the process was straightforward. I did get an email confirming, and did have to make an appointment for my interview (which took about 20-25 minutes, outside security on the departures level). But if you have enough time in MEX to take a run at it (and get back through security if you have a connection, I would say go to the immigration office and give it a shot. Normally I find bureaucracy pretty inflexible, but there is always a chance...


Sorry I can't provide more current information. I would ask that you update here with your experience when you can. If the system has gotten better, I would be inclined to take another swing at it.