Corroded Colonials...fugio & Rosa Americana

Those are awesome. The condition just adds to the character, if you ask me.

The word "rare" on that site (and I'm only guessing, as they don't seem to offer their criteria) probably refers to the Sheldon Rarity Scale, generally accepted as:
R8 = 1-3 known (estimated), "Unique or Nearly Unique"
R7 = 4-12 known, "Extremely Rare"
R6 = 13-30 known, "Very Rare"
R5 = 31-75 known, "Rare"
R4 = 76-200 known, "Very Scarce"
R3 = 201-500 known, "Scarce"
R2 = 501-1250 known, "Uncommon"
R1 = over 1251 known, "Common"

"31-75 known" sounds like a tiny number (at least, to me), but these estimates are endlessly debated, and most Fugio die varieties could be considered in the R4-5 range.
What your Fugio is worth in dollars, IMO, is not as important as the membership it gives you in the Fellowship of the Gnomon and Exergue! (all right, I just made that up, but help me keep it going if you want. Two numismatic terms that in American coinage can only really apply to Fugios!)

paddy,
I have several Colonials that are corroded. Some are worth more to me (not monetarily) than other non-problem coins in my collection :-)

That's cool!