I have some experience with devil slip ons for an '03 R6. I just chopped my pipes myself, when my roommate got jealous of the sound he ordered a devil pipe for his bike. It fit really easily, all the mounting points worked nicely. Didn't take any wrestling to get into place and it sounds sweet. His R6 really came to life with the sound of those pipes, doesn't feel any faster to me really, but sounds great.
Can't say anything about fitment on a monster, but hope that helps anyway. Just for the record I saw another R6 around town with a Micron pipe, and the Devil pipe is way louder.