I have used them on lots of flights; helps my kids to sleep great. Sometimes they tell me to remove the baby for take off, but other times they haven't said anything.

If the baby doesn’t have a seat (mine never did), they were always fine with me unclipping the chest clip and laying the ergo across my lap with the waist band still on. Baby (usually sleeping) never moved and I easily raised the straps back up after takeoff/landing. Some flight attendants didn’t even make me do that. YMMV.

Yes. And they’re life saving in airport. Also if you’ve not flown with baby yet, it’s a good idea to do a diaper change immediately before boarding.

Yes. I have used it on domestic and international flights. The child just has to be in his seat on takeoff and landing.

Are you allowed to use ergo or other baby carriers in flight? I know I have heard you are not allowed during takeoff and landing but what about the rest of the time? Flying United if that matters.