Free entrance to museums and cultural sites this summer

I've heard great things about this Free Fridays program. My family generally prefers to go to museums during non-peak times, because of family members with medical and mobility issues, so I've skimmed right past this offering in past years. Looking at it more closely though, I'm thinking some of the sites that are a little ways out of the city and/or largely outdoors might be less crowded and worth checking out. Has anyone had experience with this program?