We have implemented a solution to the problem where the crop area zooms in/out smoothly in Flex mode, so that the wobbling problem is reduced. It will be available on the upcoming updates and in the Android version as well (hint! ;)).
In the meantime, you can switch between modes while recording depending on the situation. Finally, locked mode switches automatically to horizontal or vertical orientation in version 2.0.
This argument makes sense. However, it is more comfortable to hold the phone vertically even if you are aware of the Vertical Video problem. So, Horizon helps in these cases as well.
And even if you do hold it horizontally, you won't manage to shoot a perfectly aligned shot easily by yourself. For example, if you try to get a shot of a sunset.
Even the original/stock camera app is a software app that processes the data from the CCD sensor before writing the final video file. For example, for stabilization, it interpolates the sensor input and executes image stabilization algorithms.
Horizon, processes the video input using the same tools that the default app uses to process video.
When Crisp mode is used (in iPhone 5S), we use the full camera resolution (2592 x 1936 pixels) and after transforming it we project it to the output resolution (1080p, 720p). So, the final video is.. crisp :)
This is one of the developers of the app. The Android version will be available in the following month. We are planning on running the experiment on Android devices too!
In the meantime, you can switch between modes while recording depending on the situation. Finally, locked mode switches automatically to horizontal or vertical orientation in version 2.0.