Qs about Grace F-9 U cartridge

Hello, I read here, on the forum; a long discussion about this cartridge with many enthusiastic (even ecstatic) opinions.

I would like to know is it really an absolutely outstanding cartridge and which version is worth acquiring (because there are many). I understood that a "ruby" version is very good but what about a " U " version. I am proposed Grace F-9U

in a very good condition (see pics

for some 500 usd. Do you think the price is correct?

Thank you very much

Serge