They work fairly well but they use butane. If you're out in really cold conditions the fuel won't vaporize unless you warm the can. Also, most of the time the cans are non-refillable, the reason I don't use these things.
Check out the rate of fuel use to calculate how many cans you'll need on a particular trip.

Pack....it uses the standard propane butane mix.....available from most walmarts and every outfitter. For $25 buy one and give it a try.

Here's an alternative to the butane problem... several of us in the Troop have it -- unlimited fuel that you don't have to carry!

http://www.zzstove.com/sierra.html

Yeah, I have one of those too. They work fine but mine is too bulky for me so I just get along with my Whisperlite if I can't make a campfire.

Other than the can disposal issue, I like the isobutane systems we use (Various Jetboils). And I've never had an "I can't cook with it issue" with the isobutane canisters.

If it is 30 degrees F or below we do as a practice keep a can in a sleeping bag overnight but I have only seen negative effects when a)when super scout placed a can on the snow to start cooking, it still worked but not a good choice, it was quickly decided to clear off a rock and put the stove on that instead; separate case b) under 30 degrees and c) happened to be above 10k ft and using a stove that drew from the canister in the upright (gas draw) position. At the same time we had a different stove from the same manufacturer that drew from an inverted can (liquid draw) it showed none of the effects of the stove using the upright can.

Both stoves cooked okay but the one with the inverted draw was visibly superior and had I had a gram scale on the trip could probably have measured the fuel use difference.