I think $5k for a capable 10kW AIO is not bad at all.
$5k is a 5kW Sunny Island (not counting the liquidations I've enjoyed), and its performance is the benchmark. Match the performance, at 2x the wattage, with MPPT included, for same price, and you've got a real winner.
An off-brand Chinese product for 1/3 the price of a name brand product made in China means nothing at all, unless it approaches the quality and performance.
I never bought a GoPro for $250. I did buy a Chinese dash cam for $25. Worked at first, later just recorded noise instead of image.
What is the track record of these other brand AIO?
I don't know yet what quality difference comes with a Midnight branded Chinese made inverter. Has the DIY line differentiated itself (the way SolArk has)?