I've used both the DSS pro-fit and a hog harness on my plate.
Pro-fit:
Pros: very adjustable, easy to put on/remove with the quick release buckles.
Cons: At least for me, I had a tougher time getting the plate to sit right on my back-I'm diving dry, and it took a while to adjust (I ultimately uncrossed the straps on the back, and had to get the upper straps adjusted to the right length). This could have also been due to my relative newness with the system. Once I did get things adjusted so the plate height was right on my back, the attachments where the buckles are threaded on the shoulder straps dug into my arms a bit. Once again, maybe due to my newness at this.
Hog harness:
Pros: Simplicity. I also think that the stiffer webbing works well with a dry suit, and I found that rigging it and adjusting the fit was a breeze. This may have been a result of my experiences with the pro-fit . . .
Cons: A bit harder to get out of at first, I do recall a story by one of my dive buddies who tried hers on in her living room and almost couldn't get it off . . . when no one was home. That being said, I have no problems getting in/out of it now, this really was the first couple of times.
Conclusion for me was to go with the hog harness. Simple, does everything I want it to do, and I absolutely love the way it fits. That being said, I've kept my pro-fit and would probably use it in tropical waters where I wanted softer webbing and a bit more adjustability on the fly (like, when I am wearing the plate). Tobin's pro-fit harness is very well made, and is a great product, but for me, the hog harness is what I'll use up here in our cold waters.
-Doug