So, I hoped it would not come to this, but after this seller "OG-EVKIN Official Store" has been playing with me for about 6 weeks, I want to warn other potential buyers to stay away from this seller.

I bought a OG-Evkin CF-052 hardtail frame in November of 2022. There was a small crack in the BB area from the beginning, but when I examined it again in June of 2023 (after only 500km and a hand full of rides) the crack had gotten a lot bigger.
Since there is 2 year warranty I contacted the store and sent them pictures. Since then it has been nothing but empty promises (lies?) and long silences from them.

In the first week all they did was ask to sent the pictures to their email, which I did. Nothing much happened after that. I sent multiple messages, but none were answered. After I sent a first mail to Aliexpress customer service they finally answered and proposed to send a new frame, but a size smaller and I would have to pay for shipping. I agreed to that since I am between sizes. They day after they said they would send the payment link the next day, but they never sent it, not even after I asked them multiple times.
A couple of days later they proposed to send a different model of frame (probably because it was in stock in Spain so it would be cheaper for them). Since it is a very different model, I can not use it and I declined the offer and I asked again for the payment link. They said they were going to send it on Monday, which they never did.
They never sent the link, but assured me they were working on the frame. The factory was painting the frame according to them. This would take a week. Because again I heard nothing, I kept asking them about a status update but they did not really answer anymore.
A couple of days ago they asked me to add them to whatsapp. Since that seems to be against Aliexpress regulation, I asked to keep the conversation going on Ali chat. They responded with a weird message which I interpret as "If you don't want to communicate over whatsapp it ends here"

I am really p*ssed at them and very frustrated for leading me on all these weeks like that.

In the last days, I have asked them if my frame is ready. They just say "No". I asked when it will be shipped and now they just say they don't know. So it seems they are giving me the finger and all their promises were just to keep me busy until I finally gave up...

So today my ZTTO cassette decided to self destruct...
All of a sudden, while crossing a busy road, my crank was spinning but the rear wheel was not. Seems the smallest 3 cogs had separated themselves from the rest of the cassette. All the pins had failed. Luckily the rest of the cassette was more or less in one piece and I could finish my ride without using the 3 smallest cogs.
Shifting was horrible though and the chain skipped on some cogs. I had no idea why until I took the cassette off the rear wheel when I got home. Not only the smallest 3 cogs came loose, but also in a few other places the cassette had come apart.
I bought 3 of these cassettes and not one worked very good or long. But this one was the worst. I don't know the mileage exactly, but I guess this cassette maybe had 3000 km.
I now replaced it with a SRAM GX 10-42 cassette. Needless to say I expect a much longer life from this cassette.

In summary: Do not buy it...

I got the first one when I built up my gravelbike about a year ago. After 1000 km chain and cassette were worn so bad I had to replace both...

I then got 2 new cassettes (the same ZTTO ones) for both my wheel sets, thinking it was my fault for not checking the chain sooner... I also started with 3 new chains that I wax and rotate every couple 100 km. I only used one cassette that I switched between wheelsets.

So after about 2000km the cassette is not worn yet, but is starting to make a lot of noise. Really loud creaking. Took me a lot of time before I found out it was the cassette. After reading the reviews on Ali I do not seem to be the only one... (but most of the reviews are very positive because when the cassette starts creaking you can't leave a review anymore). The problem are the rivets that hold the cassette together come loose and there is play in the cassette and this starts to make a lot of noise.

I had the other new ZTTO cassette laying around so I put that one on with a new chain, hoping I would be released from the noise for at least some time... But the first ride this cassette also started to make a really loud noise every pedal stroke. It really drove me crazy. I have since ordered a SRAM 10-42 cassette, but in the meantime I applied a lot of oil to the cassette and the previous 2 rides it has been silent. But it will only be a matter of time...

When this cassette starts to make noise I will bin all the ZTTO cassettes, mount the SRAM cassette and never look back...

Financial analysis: 3 ZTTO cassettes at 45€ each vs SRAM cassette at 85€ is not really a lot of savings...