What is the nRF Toolbox for BLE application, how does it work?

According to the introduction of Nordic Semiconductor ASA, nRF Toolbox for BLE is a Tools app on the Android platform. There is currently a 2.7.3 version released on Aug 06, 2019, you can see the details below.

The nRF Toolbox is a container app that stores your Nordic Semiconductor apps for Bluetooth low energy in one location.
It contains applications demonstrating BLE profiles: Cycling Speed and Cadence, Running Speed and Cadence, Heart Rate Monitor, Blood Pressure Monitor, Health Thermometer Monitor, Glucose Monitor, Continuous Glucose Monitor and Proximity Monitor. Since version 1.10.0 the nRF Toolbox supports also the Nordic UART Service which may be used for bidirectional text communication between devices. Version 1.16.0 added Android Wear support for the UART profile. The UI allows one to create configurable remote control with UART interface.
The Device Firmware Update (DFU) profile allows one to upload the application, bootloader and/or the Soft Device image over-the-air (OTA). It is compatible with Nordic Semiconductor nRF5 devices that have the S110/S130/S132 SoftDevice and bootloader enabled. Since the 1.11.0 version nRF Toolbox allows to send the required init packet. More information about the init packet may be found here: https://github.com/NordicSemiconductor/Android-nRF-Connect/tree/master/init%20packet%20handling

The DFU has the following features:
- Scans for devices that are in DFU mode
- Connects to devices in DFU mode and uploads the selected firmware (soft device, bootloader and/or application)
- Allows HEX or BIN file upload through your phone or tablet
- Allows to update a soft device and bootloader from ZIP in one connection
- Pause, resume, and cancel file uploads
- Includes pre-installed examples that consist of the Bluetooth low energy heart rate service and running speed and cadence service

Note:
- Android 4.3 or newer is required.
- Tested on Nexus 6, 6P, 9, Samsung S3, S6 and S7.
- Compatible with nRF5 devices
- The development kits can be ordered from http://www.nordicsemi.com/eng/Buy-Online .
- The nRF51 and nRF52 SDK and SoftDevices are available online from http://developer.nordicsemi.com
- The source code of nRF Toolbox is available on GitHub: https://github.com/NordicSemiconductor/Android-nRF-Toolbox
- nRF Toolbox has replaced the nRF Utility app which is no longer supported

Known problems:
- Nexus 4 and Nexus 7 with Android 4.3 does not allow to unbound devices.
- Reconnection to bondable devices may not work on several tested phones.
- Nexus 4, 5 and 7 with Android 4.4 fails when reconnecting when Gatt Server is running.
- Reset of Bluetooth adapter may be required if other error appear.

Know problems with DFU settings:
- Setting Package Receipt Notification to OFF or less than ~400 may cause the outgoing buffer to overflow.

26.05.2020 - version 2.9.0
* New profile icons
* DFU Library 1.10.3
* BLE Library 2.2.0