I have not used a Kelly Kettle, but I used home made alcohol stoves for years, and both a Fritz Handel Bush Buddy and a couple of bigger Pound-Shop tin DIY versions. I also have an Alpkit Koro gas stove since 2015.
The Koro has pretty much retired all the other stoves. Much of my camping is car based, but some carrying, and in the past often with a flight, so fuel could not be carried. I tend to use a filter/chemicals, or a purifier for water, rather than boiling with a stove.
The Kelly kettle is a one trick pony, it boils water, and it does so with free fuel, so if you need a lot of hot water without fussing about running out of fuel, its a good option. For instance, two or three people on a canoe trip, stopping several times a day for a brew up. It is also nice to have hot water to wash and shave, and a few twigs isn't a high price to pay. They don't actually hold that much water at a time.
Twig stoves are similar but less efficient at heating water, but more versatile in that they can cook. They tend to need continued attention to be sure they don't go out. Bushbuddy fits inside a 900ml pot, but had a narrow operating window for fuel fill.
Do the places you intend to go have twigs? One of the things that put me off the Bush Buddy was some trips to the Lake District where I stayed on some sites where there wasn't a lot of wood around, and what there was was wet and lying on the ground. There is a certain satisfaction involved in cooking on foraged fuel, but sometimes you just want to eat and be done
Alcohol stoves are similar to the twig stoves, hard to get a simmer, but easier to light, less sooty and no scouring around for dry twigs on a rainy evening, also a lot less attention needed to keep going than twig stoves. The Coke can style stoves are the lightest option, and fuel can be carried in 500ml cola bottles, which are very light. They are more fuel thirsty than gas. I haven't used mine much since 2018, Borneo, just an overnight in the jungle, it was nigh impossible to find meths in Brunei, and only in non-resealable cans. I was horrified how much fuel I got through just to boil water to heat a ready meal thing...maybe there was less alcohol in Bruneian meths!
Gas is just the next step. Very reliable, little attention, very versatile, can simmer real food, but canisters can run out and still have to be packed out when empty. That said, the canisters last a long while. I know I can do a three week trip, between spring and autumn, with a 230g canister and have some gas left at the end.