The Shimano FFS was offered in an Al cotterless design, few bikes used it and aftermarket FFS was a pretty much non existing thing so many shops never saw one.

daVinci's independent freewheeling design is pretty cool and actually fairly easy to reestablish close enough sync for those who get use to it. We rest rode a couple in the oughts when I worked at Allstar Bike Shop. Being the region's tandem specialist shop we saw a lot of tandems we didn't sell and I have done a bit of service on one. When I test rode it with a co worker (he captained due to my legs being lacking in length) the ability to freewheel wasn't a hard function to get use to. and resyncing only took a pause or two in my strokes. However it does require some frame mods to be able to install. Not for the faint of heart. Andy