Those are some of the big questions when it comes to purchasing a carbon frame direct from a Chinese manufacturer.
The bike I really wanted when I started seriously considering a carbon frame was a Canyon Aeroad. The first 105 r7020 iteration of my current TanTan X-21 build came in way under $1500, not including the Light Bicycle AR46 carbon wheels and SQ Labs seat I had already purchased for the Giant Contend AR 3 I started riding when the pandemic hit. Compare that to $4000 for an out of the box comparatively equipped Aeroad.
I have since upgraded to almost full Ultegra r8020, switched out the LB AR 46s for Scribe Wide+ 60 discs, and included a Quarq PM with SRAM cranks, and a Pro Carbon Stealth seat ($100 usd on Ebay, like new condition). Even with the Ebay parts and deals I could find here and there, all in all, I probably could have taken all the money I spent building up my TanTan frame over the last 9 months and gotten pretty close to buying an actual Ultegra r8020 equipped Canyon Aeroad.
Things I wouldn't have with it, a very good power meter, damn good seat, fast as hell wheels for sure, full cable integration, and all the experience that comes from pricing out parts and building my own bike. Considering all of the issues Canyon has had, I'd have the cash, but I would have had to find an alternative anyway. As it stands, I've been happily riding a pretty good carbon framed bike for 7 months now. Yeah, cutting the steerer ube was scary the first time I did it. But, having that experience made it so much easier the next 3 times I did it to lower my handlebars and on my new Giant frame. Yeah, one time only costs $5, which is great and the way to go if you are only doing it one time. Cost and time adds up with more changes and more bikes. Bottom line, I can do most of the work on my own bike now. I couldn't say that 9 months ago.
Warranties are an issue for sure. My "two year warranty" on my frame is only as good the customer service that comes from TanTan. Meanwhile, I stripped the bottom bracket on my Giant, took it in to my LBS, and had a shiny brand new frame two weeks later.
That being said, I'd be worried about a warranty a lot more if I was riding a bike with a super expensive carbon frame. With my TanTan, worse comes to worse, as long as the bike doesn't disintegrate under me while I'm riding it, I've already saved up enough for a completely new carbon frame. My components are going to wear out at some point anyway, so it's all about having the reserves to replace those as needed.
Just some things to consider.