That store is closed. Does somebody have a link to the Taiwan eisen AliExpress store?

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.

Taiwan Eisen used to be considered reliable, but he was reportedly arrested last year and a lot of people were left without support after placing orders. I’ve been riding an X68 since last year; TanTan won’t apply brand decals, but for around $795 USD it has performed well so far.

Some riders have been buying from RK and Polar. Their frames cost a bit more—around $1,000 USD—but they’re offering weights comparable to high‑end models. The finishing quality is noticeably better too, and the bottom bracket and brake mounts come properly faced, much like the genuine branded frames.                         

Good news.   Jerry at XZX components now has the bolt available to order on their web site.   (I wrote him a couple of days ago and he looked into the bolt's availability.)
I will order a few of them in the next few days.

https://xzxcomponents.com/products/replacement-derailleur-hanger-bolt