I need to book a one way VIE-LON itinerary, which will be flown within a separate TATL ticket issued by DL. The return portion of the TATL is the day after the VIE-LON segment.

U2 has a very nicely timed non-stop flight, with a Flexi fare that is about €50 cheaper than the next best option, KL.

KL timing is less great, primarily because of the AMS stopover, but KL flies into LCY (closer to my destination, and offsetting about an hour vs U2 into LGW). While as STE+ I'd get lounge access with KL, I'll happily trade that for a non-stop itinerary. (BA and OS non-stop timings aren't particularly good for me.)

The only thing preventing me from going with the U2 itinerary is the potential for IROPs. If something goes wrong with KL, they have significantly more options into LON, and worst case I can call up DL and they'll probably help me out. With U2, I think my options are much more limited.

So... what would the forum do?

with a day in between, take the U2 flight no question. Worst worst case, with IRROPs so bad that one day isn't a big enough buffer, buy an alternative ticket... but I think that is a very minimal risk.

Total no-brainer.

Fly the real orange airline - Easyjet.

But with that Flexifare option, I would go for it without hesitation. If ever there was a product to give the legacy airlines a run for their money, it is this one. I used it earlier this year, stepping off a VS flight (UVF-LGW) that actually landed a bit early and I was able to change my U2 flight (LGW-AMS) to a much earlier time for nothing, no questions asked. When I did it, not all agents were familiar with the Flexifare option, but they should be by now.

A belated thanks for the replies. I did end up booking the U2 itinerary.