How to get a clean device tree to build the drivers of the msm8939/snapdragon 615
One minor thing I can answer: Archos is not deceiving you by using an SD410. It's just the "platform board" is for SD410, and due to SD410 and SD61x being of the same generation and using the same core architecture, using the same board is alright.

As can be freely verified, many SD S4 Pro (APQ8064) / SD600 (APQ8064T) devices use the board msm8960, because ultimately they're using the same Krait 200/300 cores. That doesn't mean they're dual core instead of quad.

As for the main question, I think it's a bad decision to ever purchase devices from such minor manufacturers if you're looking for development, even if these devices have popular SoCs.