Vertical integration is a double edged sword. When your car is a decade old or more, and stuff starts breaking, the only vendor that makes parts for it is BYD - and its up to them if they bother selling to you, at what price, provided they still make these parts at that time.

Time will tell how cheap and easy will they be to maintain, which affects residual value at the end of the lease, which affects payments.

Nobody pays sticker price for new cars as a lump sum. If BYDs (or whatever car) are impossible to maintain, that means nobody will want them used, and residual value will be low, which means BYDs will cost more to the end user to own than a more expensive car by a different manufacturer.

Which seems to be the case for now in places like Germany, but we will have to wait and see how the situation develops and the second hand market builds up.