Eddy,
Never played or owned one, as they are virtually unknown in western Europe.
They are one of the most popular makes in the Balkan countries of Eastern Europe, where Dallape, Guerrini, Giulietti, are also common makes. I read somewhere recently that the Balkan countries are now the main customers globally for Italian made accordions, so Scandalli have obviously cashed in.
I know nothing at all about Castelfidardo, and consequently have never really taken much interest in who makes what, after I discovered that you can get the same accordion, more or less, with about a dozen different badges on it. Now, I don't know how long that has been happening, but I did notice that Siwa & Figli is a make that also has a presence in Brazil. In Brazil, you can buy a new accordion with the brand name "Pampiana", which on the face of it appears to be just a re-badged Piermaria that was made in Italy. The "made in Italy" part appears to be correct, but whether the same parts are used in construction, as with "real" Piermarias, is unknown to those who do not work in the trade.
A few years ago I bought a little Hohner accordion to carry around with me to and from the family holiday home, and it arrived complete with a German "Trossingen" quality control tag. The accordion flew over Germany maybe once or twice, but I've never been to Trossingen, and neither has the accordion.
A lot of top Balkan players use Siwa & Figli, and some of them look like the one in the photo. They are superb sounding instruments, at least for Balkan music. I also saw a selection of US players with them on the Accordion Gallery site. If you recognised one of them you could maybe ask?
Cavagnolo have used reeds from more than one Italian maker over the years, and I wouldn't have the first notion of whose reeds were in mine. Whoever made them never made as good a job as the ones I have in my Maugein, but my repairer found plywood in the Maugein, in a box that currently retails for about 8000 Euros.
Japanese cars are reliable so I bought one. Doesn't matter that it was made in Hungary and has an Italian Fiat engine, the badge is what it's all about, isn't it?
All I can say is if a brand name is virtually unknown in a certain country, then there is probably good reason for that. If it can be ascertained that a Siwa & Figli is precisely the same as a Scandalli in all respects (and who can confirm that it is?), then there isn't a problem, unless you want to sell it.
Good luck.