Stroller Frame

can infants be placed in stroller without car seat?
I’m looking for travel system vs. stroller frame/car seat option.
What makes more sense?
Would you buy another travel system?
I would buy a travel system all over again. I liked it. But with baby #2 I’m not buying one because I still have my daughters so I’ll just buy a double side to side stroller.
2011 Teutonia T-460 Stroller Frame — ANB BABY.mp4