Will it be a demanding learning curve to acquire the specifics of the C code of that tool
after getting used to ARDUINO C dialect ?
Assuming you know C/C++, and you are comfortable programming the Arduino, you'll probably be comfortable with a different IDE in about a day.
If you go with a different microcontroller (especially a different microcontroller manufacturer or "family") you'll need to spend some time studying the hardware (inputs/outputs, timers & other features, etc.). The Arduino hardware description boils it down to about 10 pages, telling you most of what you need to know, whereas the actual ATmega data sheet is over 400 pages.
With the Atmel/Arduino chips, I've only used the Arduino IDE... But, whenever I'm using a new compiler/IDE/system, my goal for the 1st day is to get "Hello World" (or 'Blink LED") compiled and running. If I can get the software installed, configured, figured-out and working in a half-day, I'm happy! There are usually a few "glitches" and "gotchas". It may take a bit longer to learn to use the various feature of the IDE. ( I'm not an expert programmer, but over the years I've done a little programming in several different languages on several different platforms/systems.)
I was AMAZED when I was able to download and install the Arduino IDE, and get "Blink LED" compiled & running in about 15 minutes!!!!
Typically with a microprocessor/microcontroller, you might need to buy a separate programmer and/or a hardware development/evaluation board. With the Arduino, you get a ready-to-run board with a pre-installed bootloader. That, along with the free open-source IDE makes it cheap & easy for hobbyists to get started.