Year-round tyres vs. winter tyres

Hello. My wife gets event. soon a new “Flohhopser” Since you drive relatively little I have thought about having a few all-year tires installed there! How does it look with these tires for the purpose of winter tire duty? On the ADAC Hompage I found that, quote: All-year tires can be seen in this context as winter tires and can only be considered as such if they carry this M+S marking.