Weighted vest for autistic toddler?

My 4 y/o son is in a headstart program and is in a special needs classroom. His teacher mentioned yesterday that they put a weighted vest on him when he had a meltdown during nap time (he gets frustrated because he has a hard time sleeping) and she said it made a world of difference. It's something I never considered, myself, because he had a weighted blanket that he HATED and it ended up getting passed on to DS3. Do any of you use weighed vests for your children and which would you recommend? My son just turned 4 yesterday and is slightly small for his age, around the 30th percentile for height and weight. I did ask the teacher what brand their vest was but she said it was donated a couple of years prior and she doesn't remember but will look for the donation slip to check.