Regular Material design checkbox (see in action here):
Checkbox button, seen this kind in few places (example):
Which of these designs is more user friendly (and technically correct?)
Is Checkbox button even acceptable?
Is it trending nowadays?
The regular material design checkbox works. Because the user will have a clear picture as to what is selected.
In button style using color as differentiator hardly matters.
If a question has too many options to chose from than regular material design works out because less space is occupied whereas in button lot amount of space gets occupied.
The regular checkbox is more user-friendly compared to button style.
The checkbox is fine to use and understood by users including screen readers. Material guidelines help improve the usability and visibility of said elements.
Never use colour alone to differentiate user options.