I bought one when I was in NYC back in October so I guess I've had it for about six or seven weeks now. I will warn you, the uke is
NOT meant to be tuned to GCEA - you will very likely berak break a string within a week tuned that high, and as you've noticed it won't stay in tune no matter how hard you crank the tuner tension down. In fact, the highest I was able to tune it (before I found out it was supposed to be tuned lower) was about a full step down from GCEA - otherwise one of the tuners wouldn't stay at pitch once I released it no matter how tight I cranked the tension screw.
After breaking a string I contacted Kala (they answered my email within about four hours, really surprised me) and the guy there said it should be tuned CFAD or DGBE because no one really makes a set of strings appropriate for GCEA tuning on a 10" scale!
I suspect that they did over build it expecting that a lot of people would try tuning it to GCEA

I weighed mine and my KoAloha concert on a postal scale and the Kala is exactly three ounces lighter than the much larger concert so, yeah, it's built pretty heavy. I think it's mostly the neck and edge joins though - the top doesn't look terribly thick.
I found that tuned CFAD the tuning settles down and stays pretty stable in about the same amount of time as other new ukes (or new strings) do. I also found that it sounded much, much better tuned CFAD than when I was trying to tune it higher. Too much tension actually thins out your sound because the string simply becomes very resistant to vibrating.
The intonation on my pocket uke is poor - the nut is high driving the strings pretty sharp at the first fret, and it's also off quite a bit at the 12th fret.
I wouldn't buy another one at this price, but it's not really a bad little box. I'll probably do a setup on it and then it will be fine for what I bought it for, which was traveling. It's small enough I can throw it in my regular carry on bag.
As you noted the build quality is pretty decent - I noticed a tiny bit of glue squeeze out where the fingerboard meets the top but that seems almost universal in factory ukes - at least, all of them that I own have a bit of that. Otherwise, the fit and finish was decent. It just really needs a setup. I suspect that the tiny, 10" scale excaberates (sp?) intonation problems. The larger ukes in the series might be set up better.
John