The "can't be linked to your identity" part depends entirely on how you get your BTC in the first place.
If you buy them with cash from a guy on the street who has no idea who you are, fair enough.
If you buy them from an exchange by making a deposit from your bank account, the level of anonymity you enjoy depends entirely on how much you trust the exchange. They know your real name and the wallet you used to receive the BTC. If they share this information with anyone, a sufficiently motivated attacker can trace the BTC to their ultimate destination (the wallet of the VPN firm). If you launder the BTC through a few intermediary wallets first, I suppose you might have some plausible deniability, but if you're a journalist in a repressive regime how much is plausible deniability worth?
