Those systems are very comparable in price used, really can't go wrong either way.
With the JB3, you can update it to 1.3 or the latest 1.4 beta for free by sending the chip in to BMS to be flashed, or having someone with a burner flash it for you. So you'll have a fully supported production system. 1.2 is pretty invisible but 1.3 is much better, so update it if you go the JB3 route.
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