Upon installing the Chrome extension and after engaging Missing mode/location tracking for the first time, you may notice a popup from HiddenApp. The popup appears when HiddenApp acquires a new location.
The first time the app receives a location, the popup will hang for a few moments. However, this only occurs the first time the app engages and is far less intrusive after that and is essentially unnoticeable.
The following screenshot shows what occurs when the extension engages for the first time: