I can only speak for my kids, who were mostly raised by their DSD. They’re adults now. They’re unbelievably close to DH. He’s always been a Dad to them where their bio-Dad has never bothered, and they’ve always appreciated this. He chose to do it.
They ring him for a chat more often than they call me. They ask for his advice and help. He’s been a fantastic role model to them. My DS is a wonderful partner to his DP and I know it’s because he’s grown up seeing a truly caring, supportive, happy relationship between me and DH. Similarly DD has high standards in her relationships. If I’d stayed single, their only point of reference for relationships would be mine and exH’s, which was utterly toxic and I’m sure the outcome would be very different.
Financially, as a couple we’ve given them a beautiful home with their own rooms, lovely holidays, and we were able to gift them deposits to buy their own homes. I never could have done this if I’d been on my own and struggling on one wage. Having a partner made it easier for me to advance my career, which has benefited us all.
DH has always done everything for them - taxiing them round, clearing up their vomit, school runs, cooking, watching them play football every weekend, etc. He taught them to drive, has done loads of renovations on their houses, and he would always move mountains for them.
I know my children. They adore him, and I know they feel blessed to have him in their lives. An example - DS recently took out payment protection insurance because “if anything happened to stepdad I’d be so devastated I’d need to take at least six months off work”, which I thought was sweet and ridiculous in equal measure! (DH has a life-limiting condition but is quite well at the moment).
That’s not to say he doesn’t get on their nerves sometimes, as do I. They get on ours at times too. That’s just family life.