I’ve always had either problems with schedules or problems with environment because it has it’s own. Cron is fine as long as you are lucky. That isn’t to say there never were problems with timers, on debian 9, I think, shipped version of systemd had a bug where systemd-analyze parsed schedule correctly and timer just shit itself. But only for some specific case I can’t remeber which, but it was extremely frustrating to debug.
I’ve always had either problems with schedules or problems with environment because it has it’s own. Cron is fine as long as you are lucky. That isn’t to say there never were problems with timers, on debian 9, I think, shipped version of systemd had a bug where systemd-analyze parsed schedule correctly and timer just shit itself. But only for some specific case I can’t remeber which, but it was extremely frustrating to debug.