I've been using a Gold Tone fretless solid body electric micro bass as my main instrument for a couple of years now. I enjoyed it so much that I bought a second which I shipped to a luthier as a model to build a custom hand made 5 string fretless uke bass. A fellow lefty drummer friend of mine also bought one and preferred drums over bass so he sold it to me after a few months of owning it. Since the basses are fretless I am able to get around the intonation issue for the most part, but you really have to be spot on since the scale length is so short and even a slight misplacement of the fretting fingers will cause problems (especially beyond the 12th fret). Although I truly detest lines and dots on the fingerboard of fretless basses, they have been very helpful in getting used to the extreme short scale of the Gold Tones. The rubber strings are another issue completely and I am still finding ways to work better with them. But the combination of ultra short scale and very low tension have been great for my decrepit fingers.
I have never played a Kala uke bass (hollow or solid body) so I can't compare them with the Gold Tone. If the Kalas are fretted and the intonation is off for whatever reason that would be a real drag. I was hoping to try out one of their California series solid body uke basses which they used to make lefty but they don't anymore.
The solid body Gold Tones sound great and are a total blast to play. No more pain in my fingers while playing nor pain in my shoulders from supporting a 9lb instrument. I can't wait for my custom 5 string fretless to be finished.
Hope this information helps.
https://goldtonemusicgroup.com/goldtone/instruments/me-bassfl