I had it for DD1. You use if when LO outgrows swaddled at 4 months or so. It's like putting you LO in an astronaut suit. They can move, but its harder for them, so they don't wake themselves up. I thought it was a good transition from a waggling to just sleep sack. At the time it was about $40.
PP describes it pretty well. We just bought it for DD but haven't used it yet so I can't comment on whether we like it or not. We plan to use it in a week or so when she'll be outgrowing her swaddle..
I used it with my son. It didnt work for him but they do offer a money back guarantee within a small amount of time. If you order one, go to their FB page first I found a coupon there.
Re: magic sleep suit