My friend Magnus Sjoquist–Swedish bass player extraordinaire–has written a pretty
comprehensive review of the Kala California and S.U.B. Series solidbody uBasses on his blog. He even included soundclips with the review.
He compares the Kala California Custom Flame Maple Top (5-string) with the Kala S.U.B. Sunburst (4-string).
Since the California 5-string has a 3 inches longer scale length the spacing of the frets will be greater. Stretch out these 3 inches and you will of course get a fretboard that is 10.5″ shorter than a regular 34″ [scale] electric bass. This makes the transition from the regular electric bass a lot easier.
I have just done some recordings and I do feel the extra length gives you a slightly more defined tone and the string also feels a bit more ‘solid’ under my fingers.
Magnus has been playing uBasses for nearly three years in concerts and in jam sessions–including with cover bands and choirs. He says they are both great instruments to play. They may take a little getting used to because of the short scale, but putting in the time is well worth it, he notes.