2 one-way tickets instead of RT?

While conventional wisdom has always been that two, one way tickets are substantial more expensive, on a recent trip this past summer we found that two one-way tickets were cheaper than a round trip. Just as you have found. Have no idea why. Maybe the computer was sick that day. Airline ticket pricing is a deep state mystery. No risk to two one way tickets. Not sure why one would be cancelled unless it you are buying a discount airline that may fold later this year.

Trying to understand the logic behind the pricing of flight tickets is wasted effort. It is what it is.

If you have found an option to buy flights at a price that you're happy with, I wouldn't dwell too much on the one-way versus round-trip versus open-jaw labels. You want to get there and back, in some manner that's acceptable to you, at a price you can live with. They can call it whatever they want.

Anyone aware of any good reasons to NOT buy 2 one-way tickets in and out of Ireland?

No

I understand that if one is cancelled I'll have to buy another ticket at its current price, but, otherwise?

If you have two one-way tickets, they are entirely separate. One being cancelled or unused has no affect on any other ticket

The issue with a cancellation is in the case where one has a round trip ( or multi-city/open jaw) ticket and fails to show up for the 1st flight. That is when everything else on that booking gets cancelled.

So others can share your luck, can you indicate the departure city?

I recently booked our two week trip to Ireland this July and was playing around with dates and noticed that booking two one way was quite a bit cheaper. We used miles and it was a lot fewer miles to do it that way ! So glad I was playing around with dates and discovered that!

Norwegian Airlines sells one ways at inexpensive prices unlike the price gouging legacy carriers who think you are either desperate or an employee whose big business employer is paying for it.

The only issue I can think of would be if something happens that required a change of dates. For example, think of a situation where airline cancels flight for extended period (e.g., Iceland volcano, coronavirus). In cases like this, airline will either waive change fees or let you get a full refund. If only one of your tickets were covered by event, you could potentially pay a change fee for second flight.

That being said, I have done two one-ways in past. The only ”issue” that I’ve run into is that I have not been able to check in online with United. The airline questioned me about my return ticket when checking in. It was not a problem once I provided the info. One time I had 2 one-way frequent flyer tickets and one time I had an outbound frequent flyer ticket on United and a return one-way ticket on Icelandair.