FB DOES give you free F-class upgrades on NW for intra-US flights (one of the most important perks of FB ^ ). As Gold you have ~75% chance of an upgrade and as a Plat >95% . For OPUP it is a different story, if Y is oversold you have some chance as Plat. Lounge access is free with FB with 40+k miles (gold) and an elite plus member you also get skyteam lounge access worldwide. So if you can't make a US-based Plat (75+k) and your objective is lounge access and domestic US F-upgrades, FB might be a good choice for you (just be aware that the customer service is close to not existing and certain low fare classes on KL/AF/NW give 25% miles only; AZ flights earn 100% miles as well as CO and DL on all revenue classes).