CO2 bottle permanent seal?

[Airplanedoc]

Anybody use these? Are they better than the nylon washer? I have the valve that will accept them, just wondering if they were worth the $3.99

http://www.midwestsupplies.com/co2-leak-stopper.html

 

[masonsjax]

Terrible. I had one on my 5# tank. The o-rings are thin and compress too easily to form a tight seal. I lost 2 tanks before I figured out where the leak was. Fiber or nylon washers work just fine. My micromatic regulator has a built in nylon washer thingy which works well, but I will go back to using standard washers when that begins to show signs of wear.