I am one of the few with a better step-scenario. My fiance and the BM were never married, they were dating but not living together when BM found out she was pregnant. BM wanted to abort, my fiance didnt agree with abortion and they then moved in together in attempt to "do the right thing" their relationship died before SD was born, BM then cheated and my fiance kicked her out when SD was newborn. BM tried for custody but didnt succeed due to lack of work and housing, she spent 2 years getting her things in order, took him back to court and gained primary custody when SD was 2.
My fiance and I started dating around this time, by the time I moved in with my fiance SD was already primarily living with her BM. BM had a few moments of "she wants to steal my kid" very early on but soon discovered that I had no intention of playing a mum role and backed off.
Generally speaking there is little to no drama. BM sticks to the CO (though sometimes likes to twist it to her favour) she doesnt get involved in our lives/our time and we dont get involved in hers.

However, BM did used to control all child care; when SD5 started school it started to feel that BM was using the holiday child care as a control game against my fiance. They have never communicated well, with both of them preferring to ignore one another, but they do when they have to.
BM started either ignoring my fiance when he asked about child care, or simply not telling him till last minute and one time she ignored him and then didnt book any care. We were able to make it work but it left my fiance feeling angry so he has since set up his own child care files completely separate from the BM, the child care were originally stand off-ish with my fiance but upon hearing and seeing the times that he had asked for confirmation without response they actually took it upon themselves to inform BM that the child care account was now split and that if she failed to confirm with SD5s father which care was booked and still booked child care on his time then she would be charged.
This was back over the summer holiday so a good 6 months ago.

Last week, BM emails asking about christmas, my fiance replies, short and polite and low and behold receives a long ranting email back from BM in which she finally says whats really bothering her. She doesnt like that my fiance didnt tell her he had set up his own child care account, since she felt she should be informed about any/everything he does regarding SD.

My fiances response? He read it and said to me "Im not replying to that, shes just pissy that she can no longer play her little control games that she likes to do every school holiday. If theres one thing I've learnt from that step talk forum, its that boundaries are our best friend. What I do or arrange for SD5 on my time is non of her business, what you or I decide to do is non of her business and Im not getting drawn into silly email arguments"

This is why I share step talk with my fiance! Its just as useful for him as it is for me to gain perspective from other peoples experiences and try to make sure we avoid the unnecessary arguments and respond appropriately when we need to.