Several flights on SCAT, never an issue. Even went to Taraz once on an AN-24. My maiden flight to KZ was on Yak 42D back in the day. Now, those old Soviet planes did make me a bit nervous but the CJs are relatively modern and again, my personal experiences which are at least a dozen or more flights have been fine. If possible, I do fly Air Astana but sometimes SCAT is the only option.
I find this to be one of the things that opinions are going to really differ on, a experienced expat that I know won't set foot on either companies aircraft. I fly both regularly.
Air Astana is 49% owned by BAE and I think a European carrier even handles their maintenance department, maybe Lufthansa? As mentioned in this thread, Air Astana is cleared for European air space, SCAT is not, same for Bek air and a couple others.
I can tell you the safety department at a large international oil company in KZ that my relative works at allows employees to fly on SCAT Boeing and CJ aircraft but not the Soviet Antonov and Yak ones.