So, I've been lurking here for some time and sometime in early May I placed an order for a X68 with complete Ultegra di2 groupset and a set of 50/65 Falcon pro turbo from Light bicycle. The wheels are 34mm wide and I run Conti GP5k 30C that expand to 33mm. It is absolutely not a weight weenie build, focus has been on a mix of aero and comfort for endurance riding without explicitly trying to weigh the bike down. Don't have a good scale to weigh the bike but the bathroom scale says it's around 7,7kg. This is without wrapping the handlebars though.
The pros with Tantan is the comparatively low costs for both frame and groupset 2100$ inc. shipping to .se. Also the possibility for custom paint. I think the cons would be pretty much everything else though.
I ordered the frame painted matte red and matte black with a long gradient along the top tube and down tube. Gradient is good and is actually better in reality than what it looks like on the pictures. However it was not matte but painted in gloss.

Paint was ok on the frame, the fork has a few marks, some small like specks of dust in the color and one larger where it looks like something has touched the fork before the paint dried. Thankfully it's at least on the back of the fork. Brake mounts have some over spray and front brake was hard to install. Had to do a lot of filing to be able to install it in the first place and in the end I got help to do a professional facing for the front brakes.
Tantan also sent the wrong handlebars. I'm a small guy, frameset is size 49 and Tantan sent me 400x90 handlebars instead of the 380 I've specified. On my old bike I run 360 so this was already a compromise. And they're absolute a$$holes to deal with when it comes to something like this. If it is mentioned that they've made an error - the emails won't be answered. If I ask for at least some kind of discount for ordering a new handlebar - the emails won't be answered. I've been reluctant to install the wrong size handlebars for a while but now I've just installed them so I can at least ride the bike.
Also I didn't calculate seat post length and min insertion so now I've got about 85mm insertion. X68 should have 100mm insertion but SL is at 75mm. Since I'm a small light guy I'm not stressing over it and anyway Tantan doesn't want to talk to me about selling me a longer seat post or narrower bars.
Has anyone tried to fit Yoho seat post to the X68? Or can someone recommend any other SL8 style seat post that will fit?
It is unlikely that Tantan will receive more money from me so I've ordered the new HBR17 in 360x100 from LightCarbon. More expensive but it looks promising IMHO. I like that it is available in narrower size and I also like that it has some flare - if nothing else it will at least contribute to a sporty look. It is also available with spacers/adapter for SL8 if you ask nicely.
So far I have only made 4 rides and less than 200km on the bike and it sure is different from my old bike. The old is a repaired Focus Cayo (2013-2014 or something) with 35mm alu rims and mechanical 10s. Even if the new bike only is "current" the leap from the old bike is large enough to make it feel like I'm in the future now. The bike wants more speed and tighter corners so I think we'll have some good times together.
Paint job didn't turn out exactly like I wanted it but I think the way it actually turned out isn't bad either. Together with the wheelset I like the visual appearance and I think the new handlebars will also contribute to a sporty/racy look. Overall I'm happy with the bike and don't regret buying it although some of the experience with Tantan has been frustrating. Only drawback is now I can't blame the bike - now it is clear that the motor is the limiting factor. I think that if LightCarbon LCR018-D had been released before I bought the X68 I might have bought that one instead and made a build leaning more on comfort (and "aero looks") than actual aero. Would be interesting to build an endurance bike with deep section rims for 38-40c slicks but that's an entirely different project.