After wearing this item for a Halloween party for three hours, I can tell you all there is to know about using this particular suit.

I am 6' and 170 lbs. I bought the L/XL. I have to say that while it did fit, there were some loose folds of material, so I can only assume a S/M would have worked for me as well. The only reason I would suggest to get a S/M instead of L/XL if you are my size is because when I used this suit to go as Slender Man to the party, I had a hell of a time making sure my (actual) suit fit over this thing. I would also follow the advice of one of these reviews where they cut a hole in the crotch to make sure that you can go to the bathroom.

The biggest problem with this thing is that you cannot see out of it. So throughout the party, I had to unzip the head and take it off, otherwise I would stay where I am for periods of time. Another minor problem, that can be avoided with diligence, is that the zipper is particularly reluctant to zip at times. This leads to the tearing problem that other reviews have noted. So long as you do it gently and with patience, you can make this suit last for a while.