The cassette speed flexibility is a big thing going for the LTwoo and Wheeltop Chinese groupsets. I really wanted to go with an 11-34t cassette on my climbing bike, but I didn't like the cog spacing of the 11 speed version and the Shimano 12 speed 11-34t cassette are quite heavy. I went with the ER9 and a Goldix 12 speed 11-34t lightweight cassette which is sub 280g. Plus the small cog spacing is similar to the 11 speed 11-32t cassette. I also swapped out my LTwoo brake calipers and went with the ZRace XG brakes which come in at about 95g a piece. I am curious if Wheeltop licensed the flat top caliper design?
I don't recommend the ER9/X for those unable to troubleshoot their own problems. I am running 2 ER9 groupsets currently, but I'm fairly methodical about my bike building and troubleshooting. If any issues are going to arise, it's all based on the RD from my experience which is basically the brains of entire system. The shifters, FD, cables and battery holder (w/springs) are all fairly solid. Also I haven't heard as many issues from the EGR, so perhaps the next iteration of the ERX/9 will have a bit more reliability. It looks like you can get the updated ER9 components individually from the LTwoo "official" store.