I have bought two sets of Keihan silencers to date. The first set was their standard issue, intended as a direct replacement for /6 models and later. They are well made, nicely finished and are as quiet as the factory items. Having traveled only 15,000mi so far, they have years of life left in them and are currently on the shelf, awaiting their next assignment which is under construction. They were originally fitted to my R90S.
The second set arrived just under two years ago, purchased direct from Keihan. They are the "Jim Cray" sport silencers, developed by Jim with the aid of an R100/7 and a dyno. Probably similar to the Staintune Sport silencers in design and noise levels. It took quite a few miles to get used to the new sound, and initially I had reservations, but they have grown on me and I now like the deeper, more authoritative "voice" the R90S now has.
I'm happy with the quality of both sets, and won't hesitate to purchase another set of Keihan silencers for the /5 toaster I'll be re-assembling next year. My only observation is that they are prone to discolour, as many S/S exhaust systems are inclined to do. (Incidentally I also have a S/S header set of unknown origin or manufacture which don't discolour noticeably, which I find quite appealing. There are no markings or identification on them though, unfortunately.)
Everything fits together as it should, and at a glance, from a distance, the Keihans look just like stock. They come with a 10 year manufacturer's warranty, but you probably knew that.
No connection, YMMV etc
'76 R90S silver smoke
'75 R90/6 hybrid
'Skills are learned, talent is ornate.' Billie