1. It constricts airflow? - Yes a little bit, not too much to worry about.
2. Should you get it? - Yes absolutely. Only for front fans of the cabinet, that are intake, air flowing to inside of your case has to be filtered for dust. Don't get it for exhaust fans, air coming out of case need not be filtered.
3 Will it keep the dust out , is it safe? Yes it keeps the dust out and it is safe.