(I have posted a version of this review under both the aluminium and stainless steel version - which Amazon allows - in case someone might find it useful and otherwise miss it)
This small Kelly Kettle is the version I use when out walking, or whenever weight and size are an issue. I find it useful not just for making boiling water - I use it to sterilise water too.
The small size is not an issue as I just refill it, and it boils faster the second time around.
I light mine with a firesteel Light My Fire Army Fire Steel for 12.000 Ignitions
and cotton wool. Pine cones which have dried out are great for getting a fire going - the pine resin makes them burn really well. With cotton wool and a few pine cones, you can immediately turn to coarse wood such as sticks the size of a pencil and then the size of your finger. You can get a fire going very quickly.
The Kelly Kettle is a stunning piece on engineering - simple and terribly effective. It creates a jet of air which enters the base of the Kettle and shoots out of the top, fuelling the fire. You start a tiny fire in the fire pit, put the Kettle on top of it, and then add sticks through the hole in the top. The fire burns far faster than an open fire, and boils water ridiculously quickly.
If using a gas cooker, you would need a cooker, gas cylinder and a kettle or something to boil the water in. The Kelly Kettle comprises all three. And there is something appealing about finding the fuel for yourself - foraging, and not having to carry the fuel.
The, err, burning question is "stainless steel or aluminium?". Aluminium has a far lower melting point than stainless steel - 660 degrees C and approximately 1300 degrees C respectively. You'll notice the difference if (when) you make a mistake with it, such as reboiling a partially full kettle thinking you refilled it when you didn't. If full, the water means the metal will never get above 100 degrees C (try boiling water in a paper cup over a fire - you can do it). If not full, the temperature of the metal not surrounded by water will soar and as soon as it reaches 660 degrees C it will melt - the seals on your Kelly Kettle will go first. It is far harder to damage a stainless steel one because the melting point is that much higher.
One disadvantage for the stainless steel version is that it can rust - contrary to popular opinion, stainless steel will rust if left immersed in water (e.g. if you store it with the stopper on with water inside). But the solution is simple: empty it after use and store it with the stopper out.
Incidentally, I bought a stainless steel one in both this size and the large 1.5 litre size. In the case of the former, the small weight difference between the aluminium and stainless steel versions was outweighed, in my opinion, by the advantages of stainless steel. I am aware that many people would prefer the weight saving of the aluminium version.
Two safety tips, if I may: when putting the kettle on the fire pit, always ensure the stopper is out. If you forget, the pressure inside the kettle rises and eventually the stopper will pop off and a jet of boiling water can shoot out . And place mugs on the ground and pour boiling water into them there - if someone is holding a mug, a simple error can mean spilling boiling water all over their hand.
One of Amazon's photos shows the Kettle being used on a wooden table. You don't want to do that as it will burn the wood underneath! Youtube has a video of someone using a Kettle for the first time - on a smart wooden garden table...