When we flew from Detroit to Amsterdam, we applied Global upgrade certificates to upgrade from economy to premium select.

Delta Premium Select Bottom Line

Premium economy is better than regular economy or comfort plus.

Premium Select is a different and better product than Delta Comfort Plus.

If the question is if Premium Select would be as good as economy, I wouldn't consider it.

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Delta Premium Select. Each passenger gets an amenity kit, pillow, and blanket but no place to store any of that stuff.
The in flight entertainment screen was large, bright, and responsive. It was loaded with and endless selection of movies. Power is readily available for each passenger.
I’m no audiophile, but I thought that the over-ear headsets provided very good sound (at least plenty good enough for movie-watching), and they were reasonably comfortable.
No place for shy elbows.
On our daytime flight from Amsterdam to Detroit, our first meal was: salad, chicken curry, and Ben & Jerry’s ice cream.  The food was fine, but nothing to write home about.  I really enjoyed the ice cream though!  While I didn’t see Delta’s economy service, my guess is that we were served exactly the same stuff as in economy.  In my experience, Delta One passengers get much better offerings.
Snack served near the end of the flight: Dutch cheese roll, and passion fruit mousse.  Both were very good!  Additional packaged snacks (not pictured) were available self-serve in the galley throughout the flight.