I have "worn hair" for 25+ years and up to a few years ago (when I started wearing the lace units) I used synthetic hair and it was great. There are different types of synthetic hair available and a couple of them are really good.
You can not bleach the knots on synthetic hair so that can be a problem.
On my custom units (I've been wearing lace for a couple of years with a lower density) I always order the gray (I get 25% or so gray now) hair as synthetic. This allows coloring of the non-gray hair (which is human) and doesn't change the gray.
Synthetic, IMO, would be ideal for injected skin bases as there are no knots to worry about.
You are correct in that synthetic does not fade.
It does act a little differently than human hair but, again, I wore it for many years (as a topper) and had no problems at all.
It's ideal for those who want a tight curl as the perm. process really cooks human hair.
Synthetic would be ideal for a full cap made with injected poly or an injected skin.
It last kinda forever. You'll wear the base out before the hair.
Lastly, it's probably a little more important to sleep on a satin pillow case with synthetic because the synthetic tends to get really messed up by pillow rub.



Fred