I've got one of them. The only bad thing I have to say about it is that the instructions are naff.
It comes with it's own socket for the monitor, so you'll need somewhere to fix it to the back of the A1200 (not a big problem if it's towered).
I've never had a problem with it using it on it's own. It played all my games happily without a glitch. The same with workbench - I was running that up to 640*512 very happily.
I don't know about running it at a higher res than that - my monitor couldn't handle any more :-)
