I've been looking at those thin travel ukes, particularly the Kala, but others as well. It seems that most of them are spruce tops. I wonder why that is?
I know that this isn't the answer you are looking for, but my guess is that they use solid spruce so it will crack when you take it anyplace that has extreme weather while on your trip. Nothing like walking off a plane in sub zero temperatures or driving through a desert to really "open up" a spruce top. And then there's rain, snow, and sleet.
And I will never understand the travel part behind a travel soprano.
On a more serious note, if are going to travel with it, you may want to find a thin ukulele that will withstand the rigors of travel. I have dropped one (padded gig bag) in a hotel parking lot and put a nice ding on the back of another trying to negotiate the ergonomic furniture arrangement in a room.
That's a good question on why the spruce travel ukes. It doesn't make much sense to me. Personally, travel uke means any decent sounding soprano made of laminate wood. As long as it sounds ok the cheaper the better. The Kohalas are my favorite cheapy painted laminate that sounds decent.