When I asked the salesperson at Penzeys about Mexican vanilla a few years back, he told me they sell a lot of it, so that's how I came about giving it a try, and I wasn't impressed.
I remember reading somewhere in the past few years that Mexico does produce top quality vanilla, however, they don't usually export it, and the vanilla the tourists buy (depending on where you purchase it) isn't the real thing either. That brings to mind whether or not Penzeys imports the real thing. I don't know, and I don't know who in this country might have a connection that allows them to import the real thing.
I don't buy imitation vanilla extract. Unfortunately, a lot of the so called 'pure extracts' are synthetic, too. Even if vanilla extract appears dark in color, it could be because it was artifically colored to look like the real thing, but in reality, it's synthetic. As I've stated earlier, I like the Madagascar vanilla I purchase from Penzeys. Penzeys also sells double-strength vanilla extract from Madagascar, although I haven't tried that.
"Those are my principles, and if you don't like them...well, I have others."
Groucho Marx