I'm not trying to say this is the best option. I know there's software-based full disk encryption products that can create encrypted volumes on flash drives, and that's probably the way I would go, but I also know that those kinds of approaches can be complicated and difficult for some people to use. There's no one-size-fits-all security, and this might just be the best option for some people. As weak as I'm sure the PIN code the average person enters is likely to be, it's probably still better than no encryption at all. This isn't going to protect your secrets from the government, but it might just protect them from a sibling, a spouse, or a thief of some sort.
Plus, it can serve as the thin edge of the wedge that gets people thinking more about securing their data.