It depends on which one it is (the Planet Phatt or the Mo' Phatt). The Mo' Phatt for $300 is a STEAL. The older Planet Phatt is OK for that price, but not all that spectacular.
I had a Mo' Phatt last year and sold it for $500 when I changed things in my studio. The Mo' Phatt has some good and unique sounds. There are a lot of basses, a fair assortment of pads, a good crew of synthy type sounds and other "unique" sounds that don't easily fit into the normal categories. The Mo' Phatt is also a good deal because of the tweaking that you can do to the sounds with the filters.
That said, I sold mine because I found that I wasn't using it very much for the style of music that I was doing. I do a lot of rhythmn-type music (from Pop to RnB to hip hop). With the type of sounds that I usually used, I simply wasn't using it very much. Another issue that I had with the Mo' Phatt is that I didn't much care for the drums. There were/are a lot of "non-ordinary" drums in the Mo' Phatt, but I just wanted a box with "straight ahead" drums... just some phatt kicks and snares and crispy hi hats. For my tastes, I didn't get that from the Mo' phatt "right out of the box". Since I didn't have too much time to work for the sounds, I bought Gigasampler and some drum and bass sample CDs.
You, however, might have different needs from the Mo' Phatt. It looks like you've got the drums taken care of with the MPC and the general sounds taken care of with the Korg. If you want something with a different flavor to use with your setup, I think the Mo' Phatt will serve you well. Don't forget that the Mo' Phatt does have 500+ user programs that you can write over and create your own programs. The user banks are the "same" sounds as the ROM banks, so you don't have to worry about writing over good programs. I simply did not have the time to tweak. With that, I'll say that the Mo' Phatt is a perfectly good module, that will find much use is someone else's rig. I just didn't have any real uses for it.
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