I think I'd ask at tripadvisor.com forum for air travel. My other source recommendation would be flyertalk.com.
Our experience with DL SkyClubs is no, sometimes even with that BP for required class of service, ie biz OR first. That's why we got the Amex Platinum card--it includes lots of goodies like unlimited Priority Pass Lounges w/out fee.
We always had to present the card plus a BP to be considered at AF, KL, etc.