To answer your earlier question: No, convertible seats don't snap into carts/strollers and the like.
Here are a few tidbits from the BB book for the Graco Snugride:
Pros: lightweight (base model), level indicator, canopy, easy to use, front belt adjuster. works with many strollers.
Cons: Only one crotch position.
Comments (I condensed this section a lot): Good fit in most vehicles. Affordable. Ease of use. BB recommends the 30-35, not the 22...says it typically too small for todays babies. Lacks some side impact protection found on expensive seats and lacks a rebound bar. Avg crash protection.