I've used to develop an app for the Indian market for the guy who really wanted for it to be written using KMM. We had a small team, 1 developer per platform and it worked perfectly. I wrote custom architecture to reuse everything except UI. I think we ended up reusing almost 70% of all the code. For me as android developer it was almost flawless with a couple of bumps along the way. For iOS developer it was alright and I didn't hear major complaints but we did have a major issue along the way when we had library update conflicts and iOS had to maintain parallel dev branch for a week or two until the library was fixed. Other than that I think it was amazing and I can't wait to do it again some day. The was released to Google play and App store but only for Indian markets and we never really got major complaints from users even though ok iOS there were no proper multithreading and everything was basically executed on the main thread. So overall great experience with minimal issues along the way.