I have not tried Rivendell's Silver Shifter which is a fairly recent remake, but am familiar with Suntour Power Shifters I have a set of downtube mounted ones on a 1978 Raleigh GP and on a 1985 Bridgestone 400, so they were around for at least that long. The cable is pulled with the ratchet action and released against friction, so in that sense they are retro friction. They were available in various finishes and styles including bar ends and stem shifters. They take a little getting used to with the ratcheting action, but very are reliable, pull enough cable for even an OT derailleur with an OT number of gears and are slip resistant. They IMVHO mark the high point in the evolution of friction shifter operation, but the Simplex retrofriction shifters are better looking.
Marcus Coles
London, Ontario, Canada.