If you fly PS at all 12.5k miles is close to the difference between sitting in coach and business. Save it for that.

UA First to Europe just isn't differentiated enough anymore unless you're well over 6 feet tall in which case more width at your feet is helpful.

Worse food than CO biz and if you're on an old 777 (very likely) worse inflight entertainment. You judge whether having to step across someone twice is a meaningful hassle. It's not hard and you have a great lie flat seat.

As Channa says if it were another carriers first then we're talking.