Dublin airport departure

1. this is true
2. correct

It is called U.S. Preclearance and it takes some extra time. It is not optional -- you cannot choose to skip it and go through immigration upon arrival in the U.S. The technicalities may have gotten a little smoother since we experienced it, but basically you have to use a computer terminal to confirm that your passport is in good order; you then see a human agent to confirm that you are who you say you are, and view a photo of your checked luggage, which the agent will show you, to affirm that yes, that is your luggage.

Depending how many people are ahead of you, it could take an extra 15 minutes or more like an extra 45 minutes or even longer.

They have this at both Dublin and Shannon (as well as Toronto and several other airports around the world). Flying out of Shannon will not enable you to avoid it.

We experienced 45 minutes or more (for just the US segment) for a morning flight to the US. The 2d carry-on check eats up some of the time as well. We arrived at the terminal 2+ hours before scheduled departure and were glad we did.

Both statements are true. I just want add that you need to allow extra time to get to your flight. We were there in September. First, you have to go through the line for regular airport security. Then, there was another security check before US customs where they x-rayed our carry ons and electronics, and then the line for actual customs, which really didn't take long at all. They did not show us a picture of our checked bags. The best part was when we arrived back to MSP, we just retrieved our checked bags and walked out to the car.

The lines to get through US pre-clearance at DUB were hellish when I was there middle of last summer (peak tourism season). While it may indeed save time upon arrival, it seemed like no net savings in time from what I could see - any time you saved upon arrival was more than made up for by the time in line to get through pre-clearance at departure.

Some potential time-saving tips if there's a shockingly long line for pre-clearance when you get there:

1. If your flight is leaving soon, don't be shy about telling the line-minders. They can grab you and whisk you through fairly quickly if needed (you will need to show your boarding pass - no cheating!).
2. If you're flying business class, there's a shortcut through at least part of the waiting (again, gotta show the boarding pass, and you'll still have to wait in one of the long lines, but once you get through that, you can skip the next long line; follow the signs and wave your boarding pass).

Can never tell with these things. We came home thru Dublin airport in Jun 2018 and the tour company had us there hours early. But all the lines - security and customs were so short there was no delay. In fact they didn't have or need a separate one for Global Entry. Things did go faster at the Atlanta end - never my favorite airport.

No totally relevant, but the line in Shannon June 2019 was minimal. Actually had to sit and wait for the pre-clearance officers to arrive. Negligible time in processing.