What's the difference if any?

LO I think will grow out of her infant car seat quite quickly! So I'm starting to look into convertible car seats. Likely will go with a Britax do want to start keeping my eye out for sales.

Where did you get your Britax?
Do you have another convertible car seat? If so, which one?

LO is 6 weeks and fast approaching 11lbs. When did your LO transition to the convertible car seat? Thanks!