Definitely better than buying an age-old iPad 2. It ought to be significantly cheaper than the cheapest iPad Air though,otherwise it wouldn't make much sense. Although, if they're priced really close, people might just force themselves to buy the iPad Air (similar to what happened with the iPhone 5c and 5s.)
This may sound naive, but I genuinely believe that Whatsapp cares about user privacy and that they won't silently mine our data and send it to Facebook. That would amount to sheer hypocrisy, and could also come under legal scrutiny. I also think that Zuckerberg, at some level, really does want to connect the world and all that, and Whatsapp is a much better bet than Facebook is, for developing countries.
That being said, Whatsapp does need to improve their security, and irrespective of the facts, this is proving to be a bit of PR disaster for them, with a mass exodus of users to Telegram. (They'd do well to nick some features from Telegram).