My opinion and experience FWIW:
i started expressing early on, (within first two weeks) to try and give us flexibility and options. DD was absolutely happy with bottle or boob at this age - no nipple confusion in sight.
When she was a month/five weeks old, we went for a two week tour to visit relatives all over the place and, as we were on the move did not bother expressing and using bottle during this time. A few days after we got back I tried a bottle again and ..... NADA. She wouldn't take it.
She is now 16 weeks and feeding almost constantly. I am exhausted and we cannot get her to take expressed milk from a bottle (on a good day she might take 1 fl oz and then refuse/cry, on a bad day she will go red faced and scream the second the teat goes near her mouth.)
I see "nipple confusion" now that I didn't see when she was just a few weeks old (she will have teat in her mouth but not give it a proper sucking action, just tongue the end of it and push it out of the side of her mouth), plus a more determined and wilful baby who now knows what she wants and what she doesnt...and she does not want a bottle!
We have tried avent, medela, tommy tippee and .... I've forgotten the name, but some "breast mimic" type, with none any more successful than the others. (thought tommy tippee closer to nature wax working, but it was first time luck).
I will try the MAM ones though as we have not tried them yet but I am afraid I am not confident.
So - at risk of going against the official advice, if I had another baby I would do bottle and breast continually from the start (unless someone could convince me better tht this nipple confusion occurs at that age more commonly and my experience was unusual coincidence), as I didn't and now I am stuck, exhausted, knackered etc. I suppose I don't know for sure that she would not have stopped taking bottles if we had not hd that break but its a big coincidence, and as i have said she was fine with both from being a week old.