Not denying the possibility that the magazine may sell your e-mail address to other places (thank God for hotmail spam accounts), but a quick lesson on magazine subscriptions:
Believe it or not, they don't make their money from your subscription fees! It's true. Magazines make money by selling advertisement space. However, in order for an advertisement to sell stuff, the advertisement must be seen. If you've never heard of this magazine before, chances are it's probably because the magazine's NEW. (DUH!) In order to be able to sell advertisements, a magazine has to have a readership. In order to gain a readership, they'll give it away for FREE. After they get a name for themselves, they'll begin the charging for subscriptions. But in order to actually sell ads, they need to be able to tell the companies they're selling to about how many people will be reading the magazine. If no one's heard of it, the companies won't advertise because there is NO readership.
I'm willing to bet that they'll sell your e-mail and mailing address to the highest bidders, too, but heck, if you've been paying any attention to the outside world (which is hard for a lot of us computer geeks to do, I know) you'll notice that the NY Times and Wall St. Journal have been giving a lot of attention to the fact that both AOL and Amazon.com have been giving e-mail addresses and pretty indepth profiling information away to companies for a long time now. In fact, AOL warns that if it goes down in the future and is sold, the buying company will have access to all of the profiled information, including collected SS#'s.
If you're worried about giving your address away to this magazine company, then you're not looking at the bigger picture. At least these guys are giving you something for it.