S4M as in the Computer case or the 3D printer ?
Me and my wife travel regularly between Germany and US with a Dan Case A4 and a Kolink Rocket case used to be EVGA Hadron Air.
We keep them in our carry. We do pack it so what we pull it out for scanning and inspection. We done ALOT of trips in the past 4 years like this.
-Worst that has happened that they wanted it plugged into the wall. (to Turkey)
-Normally they want to scan it, wipe it, lick it, touch it for traces of explosives. (So if you are a gun owner keep it away from such substances)
Once you cleared the check in its pretty much smooth sailing, unless you have a connection flight and have to recheck in, then the same routine starts again unpack it from carry on and treat it as if its a laptop.
Hope this helps. (This is between HOU, LAX, Newark, MUC, London, Turkey, Chicago)