UMI Diamond receives all updates automatically via FOTA method. You need this tool only in case of emergency (if you've bricked your phone), if you want to apply a clean install or if you want to clear all root access and custom recovery to make your phone able to receive FOTA updates again.
SP Flash Tool resources:
Flashtool tutorials: UMI Forum or YouTube guide (you can google a lot of other solutions and guides)
Official ROM download page: http://community.umidigi.com/forum-130-1.html
VCOM driver: Windows 10 already automatically can install it or you can use this: MTK_Driver_Auto_Installer_SP_Drivers_20160804.exe
Here's an optional solution to start the flashing process on your UMI Diamond if the standard method doesn't work.
It's especially useful if your phone is bricked or is stuck in bootloop.
1. Connect your UMI Diamond to USB.
2. Start the flashing process with the Download button in the flasher app.
3. Press and keep pressed the power button of your phone until the flashing process starts (red bar appears at the bottom of the app window), then release it. In this process you have to keep the power button pressed for about 10 seconds.
4. Wait until the flashing process finishes.