Are bedside (co-sleeper) bassinets safe?

Across the reviewers we read, bedside bassinets that attach to an adult bed and provide a flat, firm sleep surface are widely considered safe when used per instructions, and the NYT Wirecutter co-sleeper guide notes they offer crib-level safety with easier access. However, specialist subreddit threads repeatedly flag that the AAP does not recommend rocking/inclined sleep surfaces for unattended sleep, and parents note babies can tilt to one side on some models. Always level the unit to the mattress and stop use once your baby can push up or roll.