I haven't tried it yet, and I have to say their website doesn't make me want to. First, they mention Off the Record a lot, but it looks like they just mean the general meaning from off the record, not the popular secure Off-the-Record Messaging(OTR) protocol. Secondly, even if you could prevent the user making screenshots(which I don't think you can 100%, especially on iOS), you can still easily make an offline screenshot(take a picture). Thirdly, aside from stating they use end-to-end encryption, but they don't provide any details, not about encryption(not even "it's good because we use AES") and nothing about key management. Fourth, their frontpage seems to give the impression that the cloud isn't being used, but everything goes through their servers and there is no information on what information is kept on the server(general logs, metadata, contacts etc.)
