I still have an old, reflective slow moving vehicle triangle from the BikeCentennial organization from back in the'70s. It had two strings and was designed to be worn so it hung off one's backside over the rear of the saddle. There's lots of better devices to be seen available now, and the issue is being seen. If one sees a cyclist, it's a pretty good bet that he/she isn't traveling at 55 mph on a flat rural highway, so a redundant slow moving vehicle triangle isn't going to add any meaningful information for an overtaking motorist.