As someone else has already observed, the Hughes Autoformer will only boost the power if it's low. It won't do anything for a high voltage condition, which is the most common problem in Mexico.
On my last trip to Quintana Roo I was using a 30 amp Hughes Autoformer, and while it did everything the ads said, the one thing it didn't do was protect me from high voltage. But luckily my solar Inverter did. We were at Nututun Palenque Hotel and I had checked voltage/polarity prior to plugging in and everything was fine (125VAC). But I connected the autoformer anyway. The next morning I was running on battery power. A quick check revealed that my solar inverter had detected a high voltage condition and switched to batteries at 137 volts. I checked the receptacle again and found it was back down to 120. So I reset the solar inverter and was back in business.
The way my system is wired, all incoming power is passed through the solar inverter first. If the voltage is fine, it will siphon off some power to charge the solar battery bank and pass the rest through. It also monitors my usage, and if I'm drawing a lot of power, it'll cut back on the charge to allow more power through. If the voltage drops below 107 or rises abouve 132, the inverter shuts down shore power and switches to the solar batteries. But for either a low or high voltage trip, I have to reset manually. I've heard that the newer full sinewave inverters will automatically reset if you want to program them that way. And in a case where the power is continually high or low, it can't correct it; just shut it off and switch to batteries. So you can end up with dead batteries and no useable power.
To correct both a low voltage and high voltage condition, you need what is known in the trade as a "buck/boost" auto transformer. And I'm not aware of any of these available in the U.S. that are portable. I've used large buck/boost xformers in my designs for shore power systems on large passenger vessels on international routes, but they take a crane and fork-lift to move.
I haven't checked out the Mexican made one but that might be the way to go; if it is a true buck/boost with a protection ciruit.
(on edit)
Oh, and since all power goes through the solar inverter, and the DC converter comes after that, my DC circuits are protected also.
