I have a Behringer Ultramizer, is that the Behringer master processor you are talking about?
I just bought it at the start of this week, and this is my first impressions:
It has two separate channels with a two-band compressor, a stereo widener an exciter and a megabass-thingy (kinda like an exciter for bass). You can use each channel separately. It's pretty cheap, and it was a sale so I got it even cheaper.
Multiband compression makes compressing the mix much easier, but I noticed two bands just doesn't do the trick for me. Almost whatever setting I use I get pumping. I would probably need 3 or 4 bands to do this properly.
So far each time I tried it I decided not to use it. I am very fond of clean and bright mixes though, and usually have pretty minimalistic arrangements..

I might use it as a limiter on mixes and add some brilliance with the exciter. Also the Stereo widener works very well.
The Ultrabass thingy I didn't like one bit...
All in all: No, I don't think it does very well as a mastering processor. It does seem to be an OK stereo compressor, and the exciter is nice.