Is it cheaper to buy PE upfront or addon later? [UA International]
So I am doing a trip DFW to somewhere in south east asia (haven't decided yet) later this year. I see on google flights it is like $900 roundtrip for economy on United, and $1400 for premium economy. Is it advisable to get Economy for now then buy premium economy for the couple long legs or should I just pay the extra $500 upfront and get premium economy all the way? Based on the experience I have (havent paid much attention in the past) it looks like it is cheaper to buy PE upfront? Any conventional wisdom on this?