Do their rim brake shifters still have plastic arms + internals as seen in Trace Velo video? How is the shifting? Debating between Sensah Team Pro and Ltwoo R9 shifters
Yes, the shift lever arms on the R9 are plastic. To boot, they are riveted in, making them irreplaceable. In terms of weight, this doesn't actually change anything, and I actually think the shift smoothness/crispness is decent, despite me running full-internal routing on the shift cables.
I'm not sure what you mean with the internals being plastic--AFAIK all the mechanical shifting bits are stamped steel, and the brake hydraulic housing (edit: I meant hydraulic piston assembly) is machined metal. Really, you get what you pay for, and with the LTWOO stuff you definitely are trading quality in for weight.
I think it's important to do the cost analysis--put all the parts, weights, and their costs in a spreadsheet, and compare. At the time I bought my stuff, ultegra groupsets were scarce, and I couldn't find them as a set without the cranks, which was important to me since I needed a crank-based power meter. When I ran the math, the R9 groupset was going to be less than half the price of going to Ultegra R8000 hydraulic for comparable weight. This math can change even more dramatically if you compare bundle deals, You can get a full Ultegra build kit for ~$1000USD, which is about exactly what I spent on my R9 groupset + power meter crank + ybn chain + sroad cassette + onirii rotors + bottom bracket.
In the short months since, it seems market pressures have eased dramatically and you can now easily find parted-out ultegra groupsets on AE for pretty cheap. For example, you can easily find R8020 brifters+calipers for $500 and a derailleur set for $120USD. At that point, the LTWOO R9 Carbon+ZRACE brifter set is only saving you ~$200, and I really do believe that Ultegra is bringing $200 worth of added value in terms of quality.
So in summary, I really think the LTWOO R9 set should be reserved for aggressively minimizing costs, and it will do that job well. If you can afford the extra $200 though, I would spring for the Ultegra set