I've spent a little time with Koryuu and I like it so far.
Random observations:
Svideo looks nice. I'm sure of it now, I'm not modding my N64; this looks just fine. Chaining Koryuu through the OSSC yields pretty good results. Any issues I've seen are due to the nature of svideo--not the Koryuuu.
Moving on to composite:
Let's get expectations under control before we go further. The Koryuu is virtually zero latency. There's no frame buffer and the Koryuu isn't being marketed as a home theatre machine. It's a "zero lag" video game transcoder--and it's not a video processor. Laserdisks should be viewed using frame buffered video processing gear.
For what it is, I'm liking the Koryuu. I like the way it balances composite artifacts. All the trademark issues are still present: rainbows, fringing edges, dot crawl, and ringing--BUT: they are balanced well. Great news, Koryuu doesn't simply try to hide everything by smearing the output beyond recognition. It's got a sharp output.
My previous solutions were an XRGB-1, Extron CD 400, or a JVC SVHS.
The XRGB-1 and XRGB-2 are slightly sharper than Koryuu, but they exhibit rainbows that I find distracting. Koryuu makes the rainbows much less annoying (to my eyes) and the slight sharpness tradeoff is worth it.
The JVC was always too soft for games and I prefer the Koryuu. I have a few SVHS decks on hand (Mitsubishi, Sony, and JVC). I prefer Koryuu over all them. The Sony is too soft and there are rainbows. The Mitsubishi is sharp, but the dot crawl is ridiculous and very distracting.
The Extron CD 400 comb filter doesn't impress and it reminds me of the XRGB-1. Koryuu is better. eBay sellers might want to check themselves and mark their over priced ancient junk down to $10 or $20 usd, because Koryuu is better. Koryuu is brand new and reliable--with a working power supply and no old leaking components on the board.
I also have a couple DVD recorders, but thay wouldn't be a fair comparison, because those machines are essentially frame buffered video processors. (Koryuu is low lag.)
Anyhow... I'm liking Koryuu so far.