I have been using S1 for a year on a daily basis. I am a professional songwriter producer and think it's great. However, I've had consistent issues with midi controllers and midi sync to external hardware. I feel like S1 could really improve in this area as it's the main thing I mention to people before recommending it. If studio one could just register a midi keyboard automatically, as in Logic or Ableton, I think that would be a significant improvement. The flexibility of how it is now, should be an option. Also, my S1 never gives me midi names I can recognise to set up my keyboards. For example, my NI Komplete Kontrol keyboard just shows up as "Port 1" and My Korg Taktile shows up as just "DAW". I also have some ghost ports from my Unitor that appear. I have a port 1,2,3 that show up but don't actually exist. The actual Unitor ports show up as Port 1(2) Port 2 (2) and Port 3(2).
I have a more advanced setup than most but I don't think it's wildly different and think this area is S1s biggest weakness. Just wanted to put this forward, as I have been really impressed how much Presonus have listened to user feedback.
Ps I raised this midi issue in a support ticket, but never found a solution. Basically, I have a workaround atm, but its far from perfect.