There really is no "catch" per se. The pluses from the normal market are it has free paid app every day (some great ones in the past, lately they've been a little dumb), its faster, a lot of paid apps are cheaper, and it uses your amazon account to pay. The minuses are smaller app selection, less frequent updates, doesn't show you permissions until after downloading, less reviews, and no refunds. So really, up to you. If nothing else, its worth it for when they have a good free app.