What I mean to say is that these glasses could do more harm than good. Sure, they're dark, so your pupils will open to compensate. But that could simply allow in more UV radiation.
My advice: Quit being a cheapskate! How much did the eBay pair set you back? $10? Go to REI or any decent outdoor store and get some name-brand, sure-fire glacier glasses. They need not be expensive. REI has a house-brand pair for $39 that block 100 percent of UV and 65 percent of infrared rays. They have side shields and amber-tinted lenses. Or, for a bit more fashion, step up to Julbo's superb Micropore Polycarbonate Glacier Glasses ($89). These are a little darker than the REI glasses and are made with better, more lightweight materials.
Additionally, take all necessary precautions for climbing a very high, but non-technical, mountain. You want to be as fit as possible and get some experience in roped glacier traveling. The biggest risk is altitude sickness, particularly if you rush from Mexico City to the town of Tlachichuca and then try to dart up Orizaba.
REI's glacier glasses can be found here.