Seeing the various experiences with china vendors, I want to share my mostly positive experience with Mondince and their dealing with issues.
I want to point out - I, in my own ignorance, did not pay them through Paypal, so there wasn´t really a way to make them do anything, if they decided to ignore me.
In the beginning I contacted them through email, then moved to whatsapp. I initially ordered and got an FM336 frame - but it was from the batch of frames with glue left inside both chainstays and it was impossible to route the shifter cable through. When I spoke about this issue with Jack, he was really straightforward with it - either I manage to clear up the glue and they will send me back around 150€ as reimbursement or a new frame, if it won´t work. I managed to clear up the brake line glue, but the drive side was narrower without proper access - and it was out of my budget to get an wireless groupset, so Jack agreed to send me a new frame.
FM336 order was in march, i got it in may and by the time this all came to be, the new frames 346 a 356 were supposed to be shipping in about two weeks +-.
So I spoke to Jack, whether it would be possible to send me another frame, which he was okay with - thankfully, I just needed to pay for the fork and difference between the frame prices, since FM356 was a bit more expensive. That was at the end of May, and the molds were supposed to be ready around middle of June. Well it took quite a bit longer, but finally it´s here.
All in all, except the provided time lines, everything else was really good. Jack usually replied within an hour and answered all my questions. Reading a bit on this forum about different experiences with manufacturers, I think from the budget brands Mondince offers one of the best customer supports and actually replies and tries to help you solve, if any problems arise even after they sell you their frame.
Also both frames had properly faced brake mounts and BBs, and the headset cups were nicely reamed and faced.