I‘d like to add: „same“ and/or „similar“ in which respect? I mean, of course, regarding the size, a flat Kala and a flat Brüko are quite similar, of course. But regarding stability, for example, I‘d say they are quite diffferent. Brükos are somewhat notorious for being quite sturdy, as the used wood is quite thick (top as well as the back). Here in Germany, some say, the standard flat-back thin Brüko sopranos would be good for playing table tennis, in case you don‘t have a racket at hand, or you could even bang a nail in a wall, when in need of a hammer. From that point of view, they certainly aren‘t bad for traveling.
Regarding the broken necks ukantor/John wrote about: I heard of a few cases of broken necks on Brükos from a good friend who is into repairing ukes. But in most cases these broken necks had more to do with someone siitting on the poor instruments rather than with to small a joint. I had a flat No 5 (made of mahoggany with the maple neck) and a flat No 2 (all maple) and they both were really sturdy. I used the maple instrument for some time at work - I work in a Kindergarten and I had quite a few kids strumming away on it for hours without any trouble. It certainly took a couple of rough bumps, as you might guess. So I wouldn‘t be worried it all about this.
Well, regarding the sound, the Kala and the Brüko are certainly worlds apart. Totally different sound aesthetics, I say. The Kala Soprano travel has a smooth, mellow tone. The Brükos (and that‘s probably for most, if not all Brüko ukuleles) are famous/notorious for their harsh, percussive sound, often called the „Brüko plong“ here in Germany. While they certainly do have their own distinct sound, for sure, it‘s an entirely different question, if you like it or not.
I‘d recoomend to try to get hold of one before buying one. Or at least try a few videos on the net with an at least decent sound quality to get an idea.
EDIT: jimavery posted his vid while I was still trying to get my thoughts into a decent English... but that‘s the point, the Brüko sound. I found a different video, made by a fellow UU member from Ol‘Germany. The Brüko he is playing has a flat maple body, and a flat back (i.e. not arched), too. You can trust me on this, for I sold him the instrument about two years back....