I've shot years using either Vivitar 283 or 285 before I owned my first TTL flash (SB-24) in 1989. Both indoors and outdoors with fill flash. I currently still use an SB-22s in "A" mode on my FM2n, a nice light and compact package. Frankly I can't see a difference between my TTL shots and my non-TTL auto shots both from the past and current. And the reason for that is, for most subjects, "auto" flash still works.
Slow sync? That's a fancy term somebody coined for something people have been doing even with Vivitars and manual cameras. We used to call it "dragging the shutter". I don't see how it can be any easier with TTL. My default shutter speed for years was 1/15 sec indoors with flash, never 1/60 sec. What Nikon has done was limit the user to 1/60 sec to avoid user errors in flash situations but use a low enough shutter speed to still get some of the ambient or background light on film. At the same time, Nikon gave us the override feature to go below 1/60 sec (by obeying the metered ambient light) and called it "slow sync". Whoopee.
From this summer, FM2 with SB-22s in non-TTL "A" mode. -1 stop fill flash. Shutter speed and aperture unrecorded (I used Sunny 16 and adjusted it for the light).