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More vertical arm frames seem to be coming out. If banggood now offers copycat frames, they must see a market. I believe it is still a niche market due to the high cost. After I finish my fixed-wing builds I will probably buy one for a test build. The two that appear to be the best are the $125 Moka Jadina (Canada?)
and the $138 Karearea Kea (Kiwi):
Karearea has some interesting frames. Of course, the banggood copycats are about 1/2 the price: