There are a couple of pretty major differences. First being folders. Remmina doesn't allow you organize connections into folders. I have over 100 connections (and growing) of all different types, and folders help greatly for organization and to prevent accidental logins to the wrong box. Second is maximized window functionality. When you make a connection with Remmina, it opens up a new window, which contains tabs for each connection. If you maximize that window, you lose the connection list. With Pac, if you maximize the main window, you keep the whole app in focus, which is insanely more productive.