Li at Polar, like most sellers, claims to have the best quality frames. And they have only kits started selling that Ostro after finishing its ‘development’.
A few people on the forum have bought his SL8, and the finishing looks excellent—the frame weights are also very close to the genuine version.
The frames come with a copy Darimo seatpost and bar.
I purchased the Nexum Drag copy and can say the quality is also very good. However, one issue I found was with the stem bolts: they’re aluminium, and the head of one snapped during installation. Aluminium isn’t great for bolts, so I swapped them for titanium. I was offered replacements but declined, and suggested they consider using steel or titanium instead.
One other point worth noting: Polar and RK Ultra—also trading under the names Mirror Carbon Fibre and First Class—are actually sourcing their frames from the same place.