You see, the problem is that this is just a statement. They say they are good, no more and no less. You may want to believe this, but you also may doubt this. Mind you, I'm not saying that they're evil:-) I'm just saying that such statements cannot be proved.
Based on what I read on their Web site, their standard mode of operation involves routing the info through just one server. This is not *00&#*7; secure if your adversary has vast resources. All major Internet backbones are routinely monitored by the US and some other governments. Applying not-so-complex traffic analysis, Big Brother may be able to figure out who is behind the given anonymized connection.
The beauty of TOR (and similar predecessors, such as Zero Knowledge Systems, may they rest in peace) is that the connection is routed via *multiple* servers scattered all over the world. Additionally, TOR nodes are operated by multiple people and organizations, not just one.
That said, I believe that PP might be a good choice for basic anonymity. If, however, anonymity is a question of life and death for you, you may want to use something more robust.
Speaking of the Moonbat's comment (free vs. paid), I'd say that I wouldn't mind paying for good anonymity, as long as the payment method is anonymous, too. PP seems to offer a couple of payment options that are more or less anonymous. I'd strongly s***est not using any payment methods that may be linked to your personality, such as ****** cards.