Historically, the aisle facing seats allow for slightly more density as the seat angles needed to face the window, while still providing sufficient access to the aisle, is slightly more space consuming. However, seat designers have gotten much more sophisticated in their designs. And, the UA order provides sufficient advance lead time for them carrier to have a bespoke seat designed and, importantly, certified. JetBlue had to go with the only all-aisle accessible seat already available and certified (aisle facing) to launch the LON services.