In the ensuing years, I've bought another 10 or so, including a better example of the F6094801, which is currently the only 'double' in my Ferrari Formula collection. Most models come in either stainless / two-tone or black ion coated, on either bracelets or leather straps; the later models have further variations in case / bezel and bracelet finishes, so there are umpteen permutations. There are at least a dozen basic dial variants. One of them has eluded me for nearly 15 years. It's the black dial with red sub-dial rings and the 'grille' motif also picked out in red. I first came across them in my searches on eBay Germany in early 2010. The earliest photos I saved were captioned 'Different Black Face'. Privately I've always thought of them as the 'Black TestaRossa'. In my searches over the next 3 years, I saw examples in stainless and black ion two-tones, fitted with both bracelets and leather straps. My favourite variant became the F.609.48.25.
I've saved dozens of photos of them from eBay listings, but never been tempted to take the plunge, usually because I deemed them 'too expensive'. This was a NOS example that was listed on eBay Italy in November 2021. I can't remember the asking price now, but I later regretted having passed on it and it became something of a 'grail' watch.
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Like their humbler Seiko 7A38 siblings, prices of the Cartier Ferrari Formula CAL.531's have continued to increase, to the point where I almost gave up on the idea of sourcing a F6094825 for my collection. There was a used example listed on eBay Italy in March this year, with a ludicrous Buy-it-Now asking price of €1275 Euros (make that €1530 Euros with 20% VAT added). Needless to say it's still there unsold - item # 395299079708.
That's another thing that annoys and frustrates me, the way eBay automatically adds 20% VAT at checkout, so it's almost impossible to avoid paying it. 
However, shipping was supposed to be via DHL Express International and in my experience they will always invoice you for VAT, post delivery. I had to chase the seller for a tracking number. When he gave me it transpired he'd actually shipped it by UPS, not DHL. 