WristWeb works without the use of a third-party server for your personal data. There is no personal data being sent to me or any other third parties. WristBook simply connects to Facebook in order to link your account.
None of your personal information is stored/ can be seen by others. And none of that "none" will ever leave your devices. There might be some temporary web data being counted towards the app's storage usage but this generally shouldn't exceed 100mb. Your devices may share anonymized usage statistics such as OS version, device language etc. but - again - in no way referable to you as a person. As no personal data is being stored externally and everything stays on your iPhone and your Watch, simply uninstalling the app will remove the reference between the app and its data.
As no data is being stored externally and all data stays on your iPhone and your Watch, simply uninstalling the app will remove the reference between the app and its data.
Yes: Because the app connects directly to Facebook, basically no one but you and the people you open your posts on Facebook to. For information regarding the connection between your iPhone and your Watch, refer to Apple's documentation (it's also really safe from what I can tell).