I had a terrible experience with IB that resulted in us having to pay €3500 for flights home from Peru after an almighty c0ck up on their part (BA operated flight, issued by IB). Got the money back, eventually - but with no explanation or apology. Was the worst customer experience I have ever had, from any company. I’m incredibly cautious of codeshares since then, and won’t touch anything issued by IB regardless of saving.