They're useful for adding continuation and some other features. However, they're also a huge target for malware: potential to tamper with the binaries, discover

They're useful for adding continuation and some other features. However, they're also a huge target for malware: potential to tamper with the binaries, discovery of traffic patterns, etc. And they are absolutely clunky as a third-party app launched from the browser. I use a Chrome extension, though, Chrono. It's been very good.