they look like supertrapps. those disks you see get attached to the ends. you can vary how many disks you install to adjust backpressure. typically pretty inexpensive. look decent but have no experience with them on a monster.
It says "Made by Supertrapp" right there in the description. First line actually.
So, based on the the one person I know that has had Supertrapp's on a Duc, I would say only if really, really cheap. $100 looks pretty cheap for a set of slip-ons and I would do it if I still had stock pipes. Just don't expect them to be the last set you ever buy.
I had some of these on my bike. I actually liked them alot. Very aggressive sound. Very lightweight as well. I still have mine but am looking into getting some C/F pipes to go with my bikes new look. They cost around $360 brand new I believe so $100 would be a steel. I wouldnt sell mine that that cheap......