The Super Tacks tailbone is a little wider and longer and has more of the soft/secondary padding off to the sides than the 9K had so it seems to cover more area and help on some of those off centered landings from what I've found. The ST definitely added some much needed spine protection over the 9K, and having the adjustability makes it all the better. As for shell attachment, I just use the belt on the shell, some of mine don't even have the belt just the velcro fly up front and as long as it's the right size for me that works just fine.