Barrier windows sent a salesperson over to my house when I was looking to replace the 10 I mentioned. Maybe you were pitched by a different company, but it sounds the same. I'll agree that those windows ARE impressive, but certainly not worth 3 or 4 times the cost of a vinyl clad window. Just FYI:
Low-e glass is good for keeping the house cool in the summer, IF it's a window that gets a lot of direct sunlight (ie. south-facing). Otherwise, it doesn't do much for you.
Argon is an inert gas that is used to fill the gap between the panes and can decrease the heat loss through the window (or heat gain in summer time). As others have mentioned, it does leak out, though I don't know if it leaks as quickly as a year. It's true that it's not dangerous.
I didn't buy the windows from the salesman who came around, mostly due to price, but also due to the high-pressure, buy-it-right-now, sales pitch and the hour of my life wasted listening to him. If you have a chance to cancel the contract, I would, but be warned, a friend of mine did that and the company sent another salesperson to talk him out of it. He was not threatened, but the person they sent was not the nice, happy, polite one that talked him into the contract in the first place. Fortunately, my friend was not intimidated by the second person, but he mentioned that many people could be, so be prepared for the second "attack" in their sales arsenal and be ready to forcefully tell this person to leave your property and take his cancelled contract with him. Have a phone ready to call cops if necessary, though it shouldn't come to that.