yes, you can use it as a tablet for use with your other monitor.
If you want another monitor it would be cheaper and give you more realistate if you buy another monitor and a tablet. I use a 30in and a 24in and an intous4 medium and that is fine for me. I have a button on the tablet that forces which screen I am using for when I need to use all of my tablet for one screen.
Eh, I’m not a fan of the cintiques personally. Years of using tablets and now I am used to not having my hand in the way of my work when I draw/sculpt/paint. I have a 24in cintique at work that I let my intern use because I don’t really like it. Everyone else in my office loves it though…but they are all young whipper snappers.