by way of update, the 3rd derailleur (er9) that died on May 18th, I'm yet to get ltwoo to provide a warranty replacement. it died like the others, for no reason.
someone suggested that - somewhat magically - resetting the whole thing with new batteries could fix the issue, it didn't on mine. I capacity tested all the lithium batteries i put in these groups, i'm pretty familiar with lithium things so i doubt there's something obvious that i missed in the battery department.
So it's now Jun 21st and my reseller is saying that ltwoo support is now full on ghosting him. He's now trying to speak with the sales rep. He says he's pissed off himself that the company is behaving like that. Now my reseller isn't reactive at all, i have to chase him 5x before he replies, but i do believe him when he's saying that he's being ghosted.
i've now put over 5000 km on mine, and other than charging problems, it's been flawless. my friend who broke his wheel weeks ago is now back on the bike, so he's ticking miles on the 5th RD, so far with no problem other than calibration to avoid chain drops.
I've installed 2 replacements and these have been working fine, but that's on under 500km together.
the worst thing in all this is the behaviour of ltwoo. a beta product with a ghosting manufacturer is just bad news.