I use one quite a bit, it really slows the boat down when fishing in the wind. I got mine at BPS for like 25$. The one I have works for my 14' aluminum with 9.9. If you have a bigger boat, you'll need a bigger sock. They have different sizes.
Just throw it in and have about 6 to 8 ft of rope., I tie mine to the oar mount at the center of the boat,that way you drift with the wind, but the boat stays at a 90 Degree angle. both people can fish their end of the boat without flipping around and stuff...there is a small rope at the small end of the sock, so when you want to pull the sock out, you pull the small rope and it flips the bag backwards so you're not pulling a bunch of water into the boat.
I've even used them when trolling for walleye to slow the boat down a little when the wind is pushing you..
I think they are great.. especially if you don't have a trolling motor..
hope that helps.