I would assume that each of the scale lengths requires a different string gauge/diameter as tensions will be very different. So for the above mentioned Freemont Blacks, Worth Clears & Browns, and Aquila Reds for what scale lengths are they available?
If one gets a nonwound low-G string, it will have a much greater diameter than the high-G string it is replacing. Since the nut slot for the high-G string is normally cut to handle the diameter of the high-G string, the nut slot may be too narrow to properly fit a nonwound (larger diameter) low-G string. If one tries to "stuff" the nonwound low-G string into a too-narrow nut slot, the string will most likely get pinched during tuning, thus causing cuts in the string and premature snapping at tension. The only cure is to widen the nut slot, which one may not want to do if one intends to someday return the instrument to high-G tuning.
Wound low-G strings are usually pretty close to the same diameter as nonwound high- G strings. The nut slot issue is why wound strings are popular.
I find that surprising. I only have one uke that I bought used with a wound string, and when it unraveled I replaced it with an aquila red and didn't find a change in thickness at all. But yeah they are definitely much thicker than high-G strings and may need some bridge and/or nut slot work done.