There’s another one (Covert Browser) that’s been in the store since November that’s got a few issues (lack of cookie support, lack of POST support) that render a lot of websites useless.

Generally I don’t think this is (on the face) any worse than a regular third-party browser app: Other apps (games are a great example) are free to implement custom communication protocols and there are plenty of unsavory / underground / illicit websites on the regular internet. Tor has a lot of legitimate and illegitimate uses, but that can pretty much be said of web-based communication in general.