I must admit I was surprised how well it worked one time when we were in some moderate upstream winds. 13' oarframe boat with 2 people and gear for a 3 day trip... one 5 gallon bucket tossed out in front of us made a noticeable improvement to downstream progress...
I have one from minkota (the electric motor folks) that I have yet to use. Should be bad ass in theory. Bought it for a deso trip and then had virtually no wind issues. Its a nylon fabric cone at least 2 feet in diameter and probably three feet deep. To me its most important feature is the webbing strap on the small downstream end that allows you to pull from that end to "spill it" so you can get rid of the pull real fast if necessary. Was reasonably priced and weighs almost nothing. Packs small also. Cant wait to try it out.
I have tried a sea anchor or bucket multiple times here in massachusetts. Sometimes it works pretty well, but the hassle of setting it up can be a pain.
Obviously boils and swirling current mess with it.
You need the upstream most part of the raft catching the most wind, and the sea anchor on the heaviest/deepest drafting part of the flotilla. If not the rig will spin around between wind gusts. It still requires a navigator with the oars or an occasional paddle stroke to keep it going.