Car seat question (forward facing vs 5pt booster)

So I’m mostly asking out of curiosity as we’re hoping not to have to move our almost 3 year old out of her graco extend2fit for at least another year when baby number 2 no longer fits in the infant carrier. She is maxing out on the rear facing options, and we will be turning her forward after her 3rd birthday.

I’m looking for opinions on forward facing convertible seats and what the difference is between a 5pt harness forward booster and an actual forward facing seat?