I've got the 2.5 pint version and the accesories.
It's very light and weightwise is no problem to carry around, though it is big, so you probably won't carry it in your rucksack as I have done several times in my oversized rucksack. You can indeed only boil water in it, but you can perfectly use the base to put a pot on and use small sticks for fire. I've done it several times and works quite good. There are others like cyclist on this forum who cook on top of the kelly kettle while it's busy cooking water. Just keep enough water in and you can stay cooking on top of it.
cyclist also cooks his food in a pot cozy, so it's possible with some effort to make your entire meal with just boiling water.
I said I bought the accesories and I have found they are not worth the price. The 2 cheap aluminium little pots, potholder and a little grill have not much use or can be found cheaper elsewhere. I only a few times used the grill, once I first burnt a lot of oak in the KK for quite a while and then put the grill on the base which was ofcourse full of very nice coals, perfect to put some meat on. Another time I just burnt quite much oak in the base (no kettle involved) which I had stapled, then when it burnt down I put the meat on the grill. Worked fine, though ofcourse the fire burns better with the kettle on (chimney).
I do think the base could use some more airholes, as the wind often turns around where I am. It's not hard to drill one whole more in.
The kelly kettle is a bit too expensive for what it is I think. But nevertheless I do use it often to boil some water quickly and make a cup of tea at home ( I don't take it in my backpack anymore! just use a billycan). It's really fun to use and a good excuse to make fire. I think I would opt for the smallest version if I'd buy again, because when cooking water in the KK you can easily poor out the cooking water and put new fresh water in. It won't take long before that's boiling again because the fire was already going.
Before I bought the KK I read some comments that it would boil water really fast with very little fuel so I did have a bit too high expectations. Though it is efficient it's not magic and takes ofcourse quite some fuel.
Also my KK did start leaking after something had bumped into it (when the base wasn't inserted, the KK is much stronger when the base is inserted as you'd normally do when transporting it). I did manage to make it watertight again using pliers. I was very scared that the expensive kit it is would already be broken. The KK is made to be very light and it's fragile because of that. The quality is good though and you shouldn't have problems when being careful with it.