While I don't disagree with anything you've written, depending on your risk appetite there is a difference between compromises that require physical access and

While I don't disagree with anything you've written, depending on your risk appetite there is a difference between compromises that require physical access and those that don't - not that I think this particular product is a good idea at all, but not everything needs full local security. For some users a secure messaging protocol that protects messages as long as Alice & Bob's machines aren't rooted is Good Enough, and I don't see anything wrong with creating a product that offers this (as long as it's made explicit that this is the case - Google's End-to-End is a good example of providing this level of security and being clear about this limitation). Also, re: metadata, I really liked the work in Pond to massage the data stream so that it didn't look like encrypted data, which while certainly doesn't solve the metadata problem is one step along that path. And yes, it does use a TPM if available. I'd be very interested to hear more about TPMs that are open, well audited and trusted, if such a thing exists.