I find CO2 works more effectively with high pressure 700c tires. Not so much with lower pressure 26". They can't seem to fill the volume that a fat tube requires well. Need a few cartridges.
Whereas they have strong psi to fill the thinner 700c tires in the way, a mini pump would begin to get difficult to work as it advances 80psi+.
So for low pressure tires, a mini pump is fine whilst CO2 are great with roadie tires. YMMV of course.