For warmup yea, aim servers are great for warming up due to the intense aiming like i said earlier. I'm talking about training aim though and you said earlier that aim maps are the best to train aim which is what I disagree with.
Aim maps are definitely more effective time-wise to improve your mechanical aim (not getting shot from behind, a lot more kills per minute) but you can only improve on a handful of things were as in ffa you practice your aim in much more various ways that can be useful in matches. Best thing to do is obviously to combine different types of practices rather than only doing one, if you're ONLY doing aim maps and aim_botz your natural aim might be good but you won't have good enough movement to compensate for it. If you're gonna practice your aim for 30min-2hrs you should probably dm, if you're going to warmup your aim for 5-10 minutes before a match then aim maps are great.