Finally got around to doing a mustard slather. I did a 5 pounder the other day (sorry, but my camera is kaput at the moment). The main difference I found is that the bark is thicker and harder than my palm sugar slather. It's kinda like the difference between a thin piece of zwieback and a saltine cracker. While I like a good strong bark, I prefer the slightly ligher and thinner bark I get from the sugar. When you pull the pork, the bark almost "snaps". Edited to say that I meant that the bark almost snaps with the mustard slather. It's almost like snapping a thin piece of stiff plastic (overstated for effect) as opposed to the palm sugar bark which sort of just tears apart. I found that the progression of color was about the same. At the halfway point, both still had that mahogony color and both ended up pretty black by the end. Both really develop their dark black color in the last two hours. I'm not sure that I'd be able to tell the difference in flavor in a blind test, but I think I could identify which was which by the texture, especially if I was pulling it personally. I think I'll stay with the palm sugar unless I just want to do something different. The palm sugar is a great carrier, plus I use it in other cooking, while I rarely use yellow mustard for anything. I never put on a burger or a hot dog and when I cook, I usually use grain mustard or Grey Poupon. However, I might use the leftover mustard to revist my childhood and do some mustard coated baked pork chops sometime. That was one of the things that my mom used to cook.