Your opinions about KOETSU URUSHI BLUE or VERMILLION

Just curious, why Koetsu is so expensive, what is the technical advantages? I remember Garrott brothers, who rebuild them and retipped them for the clients, often commented about poor build quality of those cartridges (made at that time by Sugano-San himself). Now it's not even Sugano-San ...  

Even lower model are extremely expensive compared to many great cartridges with reputation. 

I have never owned any of them, but i wish to know 

Mulveling, The Rosewood Signature Platinum weights 3 to 4 grams less than a stone bodied cartridge and requires a heavier tonearm to get the same bass impact. Bass and "impact" are the two most sensitive characteristics of a cartridge, the easiest to mess up. Resonance tuning is a real issue here. I think a lot of people miss out on it because most systems just do not go down that low. Not trying to insult anyone but it is hard and expensive to get a speaker/room to go below 40 Hz effectively. I had to build my own house to get it right. Anyway, the RSP bops just fine if you get that resonance frequency down under 10 Hz. I have never compared it directly to a stone bodied unit but the motors are the same and the only real difference is the mass of the cartridge which can be compensated for. Trying to put a stone bodied Koetsu in an arm as heavy as the 4 point 14 would be asking for it. The arm would go airborne with the first warp. I believe the stone bodies came along to make the cartridges perform better in the lighter tonearms that most of us use which are compatible with the majority of cartridges that are of medium compliance.
Chakster, they charge that much because they can get away with it. There are also several middle men. I think Ortofon has much better quality control. My Ortofon Windfeld Ti will track circles around my Koetsu and is by all accounts more neutral. 

@mijostyn 
I've run the RSP on a Fidelity Research 64fx, an FR 64S with a 20g Ikeda headshell (that's more than enough mass for anything), and a Graham Phantom II Supreme. I think the stones are better. 

I have never heard the Vermillion, but have owned the Sky Blue.
The Sky Blue had good dynamics and real bass "slam", but was a bit too euphonic for my taste, mounted in an SME V. 

I’ve got a Vermillion which I use in an FR66s arm; it’s a really nice cartridge, very holographic, great dynamics, excellent tracking and minimal edge or nastiness to the sound.
Compared to my other Koetsu, a Jade with diamond cantilever, I’d say the Jade has a more “authoritative” feel. With the Jade you get the same as the Vermillion in terms of all the things listed above, but there’s something more explosive and solid about it (in a good way :)). One thing that is palpable is the lower frequencies with the Jade, the bass is really good, the best of all of my cartridges in that regards. That’s not at the expense of midrange or higher frequencies , just something that really stands out.