So I'm running an unofficial demo for 5th for some locals. I was wondering should I just use the in book archetypes for premades or make some myself for the players? Do you think the pre mades in the book are even playable?

The archetypes have some problems, ranging from glaring errors (the street samurai is way over on money, the combat mage should have an Edge of 7 rather than 2) to omissions that aren't obvious at first (the covert ops specialist is missing the locksmith skill).

I don't know if those problems would matter much for a demo, though. The archetypes may have some errors, but they at least more or less resemble their purported roles. Just keep in mind that archetypes tend to be weaker than characters that the players make themselves, and scale back the challenges a bit.