Hi,
It really depends what you want the Kettle to do.
If it’s just boiling water for the two of you - drinks, pot noodles etc. and washing/washing up then it really doesn’t matter which one you buy, they all work exactly the same way with exactly the same efficiency.
You need either a 1.2L (2pt) or a 1.7L (3pt) litre Kettle.
You can ignore the chimney cooker unless you are cooking something very quick. The problem is that the Kettle only gives you a few minutes with your frying pan before the water is boiling. Then you have to deal with the pan and the boiling kettle at the same time. You can’t run it empty and you wouldn’t want to be frying with the water boiling out of the spout. That is why Kelly Kettle introduced the Kelly Hobo accessory. It weighs virtually nothing, packs inside the Kettle taking up no space and gives you a stick stove that will cook anything -
I’ve made yeast bread on mine.

They all have legs if you want legs. I have found them to be a nuisance but that’s the personal preference of a wild camper.
You will be carrying water anyway. A single fill in the Kettle won’t make any difference. None of the established versions have screw caps. The whistle is equally useless as you’ll be attending the fire for the short time that the Kettle takes to boil anyway.
I do not know anyone who has seriously burned their fingers. We all understand fire; the instructions are simple and obvious. You’d only do it once
A look at my Avatar will tell you the my preference is the Kelly Kettle. (The little one pint Trekker with the Hobo is all that I need.)
They have so much experience and are constantly developing their product and accessories.
If you choose Kelly, I thoroughly recommend the Hobo stove accessory.
Also they have just brought out a robust bag for serious users. I have previewed a prototype
HERE. I’ve only just received it and will take it out for a few days tomorrow. At €20 it is very good value and hold so much more than just your Kelly Kettle. The web page attached to the link is well worth a look.
It’s your choice and for water only - it simply doesn’t matter.
There is a certain antipathy towards Kelly that I don’t understand. After all the Kelly Kettle is the one that they are all trying to emulate.
Edited to add:
If you are new to this type of stove then you will need to learn how to use it Just as you would with any tool that is new to you. Practice before you use it in earnest.
Tip - cheap secateurs are a useful accessory.