I am fortunate to have two of Randy's 4 string convertible fretted/fretless basses. The build quality is beyond any other bass I have played and these are absolutely the best basses I own.
After years of trial and experimentation, Randy's system has been awarded a patent. Many cool features but not easy to make these basses. For example, to go from fretted to fretless mode with a compound radius neck, every fret has to be individually machined to a different height.
I am not a good fretless player and IMO these instruments are awesome learning tools. I can switch instantly back and forth between fretted and fretless modes to check intonation. Also if I find myself drifting off pitch in the middle of a performance in fretless mode, no problem, push the lever and the frets rise - bang, back in tune. I have had occasions to switch modes in the middle of a tune because of the changes in an arrangement or can easily switch modes anytime during a set.
Since the convertible bass is essentially the same (strings, woods, electronics, etc.) regardless of mode, the differences when switching are be more subtle than with separate fretted and fretless basses.
However, I have some very nice fretless basses that sit in the corner because I don't have the chops. With the convertible basses - I can have some fretless chops instantly!