Honestly so useful. Wish I'd bought this years ago! Makes recycling canisters easy!I use my jet boil to make coffee on day trips on my bike or in my canoe and this allows me to recycle the canisters.This little tool is ingeniously simple and works very well. Super easy to tie to your pack and have handy when needed to discharge any remaining fuel so the canisters can be safely recycled. It's really three tools in one very small device. It features a threaded valve relief to discharge any remaining fuel, then, while still attached, a few quick presses down around the top punctures the canister for safe recycling. Once you rendered your canister safe for recycling you can use the bottle opener to enjoy your favorite beverage. This is an easy product to recommend.First one we ordered was mishapened and the nozzle attachment would come off. Sent back and replaced quickly and easily.The tool screws on the top of a canister and leaks out excess fuel/pressure from a small hole in the side. Once empty, press down and puncture the canister a couple times around the top and its ready to recycle. Make sure the protective plastic sleave is removed from the sharp end before doing so.Works great, just a bit pricey for what it does...its a can opener. You can easily depressurize with most fuel burner attachments that you use then use a pointed can opener to do the same thing. You're paying for convenience, and it works well.Really like having this, well worth its tiny weight just to safely vent and pop a canister for disposal or recycling (depending on your area). Garbage works don't need any more unexpected excitement in their lives.And remember, before using it--take OFF the plastic 'sheath' over the puncher part before punching. That should be obvious but sometimes is overlooked. And BEFORE you punch, vent completely. Sure, you might have no problems using a nail or something, but I've seen people's injuries from that 'one' time stuff goes Darwin Award. I prefer error on the side of caution.It doesn't work for me to empty the last two butane canisters even they were the same standard design. I still have to risk my safety by punched holes on the canisters with a nail to let the gas out. Returned for a credit.It's smaller than I had thought. Fit and finish is excellent.Now I have a foolproof and safe way to puncture and dispose of gas canisters.Yes, you could just bash in the gas canister with a hammer, screwdriver, rock etc. but I just can get myself to start hammering away on gas canister that may still have some residual gas inside it. I think that's about as stupid as smoking while filling up your car at the pump! Yes this thing costs about 10 bucks (with shipping), but that's a small price for safety in my book.You screw the device on to one of those Jetboil, MSR etc gas canisters and then push down on the lever to puncture the canister. You may hear some venting when you screw on the tool, that's normal. There is a little hole on the screw on attachment that let's any remaining gas vent safely before you puncture the canister.Great little device. I am an avid recycler and I could never bring myself to toss the used canisters in the trash, so I had a bucket full of them after only a few months of camping. This little device is inexpensive, well made, and does its job perfectly. The only minor warning is that the very first time you use it, if you are going by the instructions, you might do what I did and try to puncture the thing without removing the little protective cap on the blade. Seems obvious once you do it once but when you haven't used the thing before it isn't, and the instructions don't say boo about it. Other than that, I would heartily recommend this item.The screw on valve came lose from its holder a couple of times ' but the action is smooth and easy '.I would probably recommend getting a case for it so that no parts get lost or separated ' but over all it works well and a tin opener doesn't work cos the metal cans are too thick ' so it's worth the money '.We are running a campsite so wanted a tool to enable gas canisters to be recycled. Work great on the ones it fits otherwise not helpful.As others have reported, it works ut for how long. The centre bit keeps freeing up. Could do with a more hardy construction.Very simple piece of kit and totally recommend this.Easy to use, just punches a hole in an empty gas canister, to enable it to be put in household recycling.It is a great idea and it works well unless you put it in the hands of entusiastic colleagues who highlight it's slightly flimsy attachment.