Alright! I think I can now give some thoughts on my eR9 experience. I have now ridden ~400 km over a few rides, one of which was a ~125km ride. I am now using my previous Shimano 11-speed cassette. I guess my take will be similar to what Trace Velo, China Cycling and GC Performance have said; when it works, it is amazing! Shift is smooth, especially when indexed properly. I don't have any issue shifting under load. Though I am only a 70kg rider with max power of ~950W.
So far, I have not had any issue with my unit, except the faulty cable, which LTWOO sent replacement part promptly. My interaction with LTWOO on Aliexpress has been non-optimal, because of the time zone difference and they seem to reply only at certain hours of the days. So, my suggestion if anyone is running into issues is to be precise, concise and easy to understand, as they seem to be using Aliexpress translator for the communication.
A couple of things that I noticed: while the manual trim works, there is no way to switch back to the non-trimmed position, unless you go to the next chainring and back. This should be easily fixed with a firmware update. Another thing I noticed was that battery life is not that great. From a full charge, I could only get ~400km. I am not sure if this is from the battery or just because it is the first battery cycle. I will have check for the next battery cycle.
Installation of the groupset cannot be any easier than installing Shimano Di2 as they are identical, even down to the mineral oil for the brake. The only difference is the way it is bled. LTWOO has another air outlet which should make it easier to bleed. As long as you follow the instructions that LTWOO has on YouTube, you’re good. The brake also feels amazing, I don’t notice any significant difference to modulation or stopping power to a similarly well-setup Shimano brakes.
Overall, I am happy with the groupset and I certainly hope this won’t change anytime soon.