I have a Sit n Stand and wouldn't trade it for the world for those first few weeks after the baby was born. I have the same brand stroller as car seat, so my carrier snaps onto the cup tray on the front seat. I don't know how the ones work that don't have the little groove to snap in so I'm no help there..
When the baby was born, my other son was 4. Those first few weeks of slow walking around the block to calm the baby were great to have the seat or the board for my older son since I wasn't comfortable letting him ride his bike while I walked. Now the baby can sit in the front seat without his carrier and my son still sits or stands on the back occasionally. He is 5 now so we don't let him in the stroller for walking the mall, etc, (I use a single stroller for that) but to walk around for a long time or where it isn't safe we still use it. I don't see it as much as a necessity now but in those first months it was a necessity for sure. Now I want my son to get his exercise so we make him walk or ride his bike, but if I'm going on a 5 mile walk around the neighborhood, no way I want to hear him complain how tired he is the whole time.
I probably could have lived with just my regular single stroller for the big one and worn the little one, but in order for me to get a shower every day, I walked the block until the baby was asleep, then left him in his carrier in the bathroom while I showered so it was a win-win for everyone. If I had worn him, I likely would have woken him up taking him off to take a shower.
I got my stroller second hand from a baby resale shop for $70. They are normally $115+.
From my iPhone, probably while BF'ing.