Back in th early 90’s I purchased a Spare Air. They were fairly new on the market then and seemed like a great idea. I was living in Hawaii at the time and thought it would offer a sufficient back up air source. Without a doubt the worst scuba item I’ve ever spent money on. It would never fill completely from my main tank. I ended trading it for a new mask and snorkel. I still have and dive with both. I’ve recently purchased a 19 cf pony and that I am very pleased with.