Interesting. I looked on the MercadoLibre listing and found a couple of different products with more or less the same description and part number but the picture they provide shows something different.
Corrector De Voltaje Sola Basic 15-81-120-4000 4000va +c+
Corrector de Voltaje Isb 4000 Va Sola Basic +B+ Modelo: 15-81-120-4000
The difference I see is in the +C+ or +B+ shown in the number. One of these has a sealed case and the other has lots of vent holes. I am not sure if there are any other differences.
Ours is the one without any vent holes - a sealed case - meaning weather tight. Since we position ours outside we would definitely want the sealed case model.
I think the price is right as with today's exchange rate it comes in at about $200US give or take $10 or so. I think that is a good price. They also show the 8000 at over $300 which I think could be high priced. But as mentioned before - for most of our needs in Mexico the 4000 should be plenty.