Previously I used a simple pressure adaptor which had to be lined up and depressed for both cannisters. While it worked ok (although fiddly and gas often escaping and the adaptor getting cold quickly), eventually the points wore.This one being screw type on both cannisters keeps the seal. Screw both ends onto either cannister just as you would when using them e.g. if using the long cannister type, it should be aligned with the bit sticking out to match the head of the cannister and then twisted (only that part so make sure to hold the rest of the adaptor so that it doesnt turn at the same time). It goes on top. Then twist the handle, simple. Make sure that the donor cannister is warm. I noticed that the cannisters did not get cold like when using my previous device. You will know when you are done as the noticeable noise of the gas entering the receiving cannisters reduces to hardly anything.As with all of things things, make sure that you are in a safe environment and do check that the receiving cannister is not being overfilled despite the above comment.Very pleased. Did 3 cannisters really quickly to almost drain the donor cannister.