My daughter had been in Merlin's Magic Sleep Suit from 4-9 months (worked WONDERS for us). Around 8 months I attempted to put her in her crib without it (using the Nested Bean sleep sac instead)...2 hours later, she won and I put it back on her. Since then I've been afraid to try to transition her out again. She just turned 9 months and i felt like it was really time to retire Merlin, so I purchased this. It's a similar weight to Merlin's suit, and I just went for it. No problems at all! We're on our second night and she's sleeping like the little babe that she is :)