I know very little about Roto. I have a vague notion that Roto was the components brand of an Italian company called Rampinelli(?), which also owned a brand called REG, which sold literally tons of cheap, relatively nasty, bicycle accessories. I remember tacky chromed steel bottle cages, terrifyingly thin, squashy, plastic bottles, spot-welded steel rear carriers etc. etc.. This notion may, however come from the fact that Roto and REG were both imported to the UK by Ron Kitching, were found very close together in the Ron Kitching catalogue, and always seemed to be inexplicably displayed together on Ron Kitching stands at trade shows.
In terms of derailleurs, I have a very unreliable memory of seeing an early Roto model that was a copy of a Campagnolo Record. I think Roto may have manufactured this in the late 1960’s.
The most famous (infamous?) Roto derailleurs were the jazzed up copies of the Huret Svelto. The combination of these slightly ludicrous Roto derailleurs and the surreal tackiness of the REG products always made me think that the people at Rampinelli must have had a wicked sense of humour.
By 1982 Roto had two new derailleur models, the Roto Competition and the Roto Scorpion that was a madly cubist derivative of the Huret Eco.
There is currently an Italian company called Roto, based in Monterenzio, near Bologna. Eerily, it sells bottles, bottle cages and all manner of relatively inexpensive bicycle accessories. It is a modern equivalent of REG - and so may be the same outfit. Unfortunately the quality looks much better - so I fear that the ironic sense of humour may have passed into history.