Just a few short lines to let you know that for me the upgrade from plain 2.4.4 to p1 went really smooth.

I have the following plugins installed:

• bandwidthd (0.7.4_1)
  
• iftop (0.17_2)
• net-snmp (0.1.5_2)
• ntopng (0.8.13_3)
• Open-VM-Tools (10.1.0,1)
• suricata (4.0.13_11)

All plugins had been updated some time ago and thus prior to the pfSense core, which is not recommended. In my case, though, it did not cause any issues. This was a pleasant difference to the upgrade from 2.4.3 to 2.4.4 (also see this video on YouTube), where the fact that plugins had been installed was cause for a completely broken system after the upgrade.