The Miracle Blanket is awesome! I had my baby in it until he was about 7 or 8 months old, and then we transitioned him into a sleep sack. He also wouldn't sleep unless he was swaddled. I was a bit nervous about it at first because it felt like it was putting him in a little strait jacket, but he seriously slept SO much better with it. (Side note, he is a large boy, and 98% for height, but I still managed to fit him in it. When he got to about 7 or so months I would just leave his little legs out of the bottom part so they wouldn't be too scrunched up, and just swaddle his upper half. )
He was a little houdini in all the swaddles except for the Miracle Blanket. Definitely worth the money. Get 2 (or 3) at least so that if it gets wet or dirty at night you have a back up plan. Actually, even just for laundering it, because I never could get a load washed and dried in the space between his naps.
Good luck!