> RPi A+ is quite light, so RPi+Navio weighs as the normal autopilot

Not to detract from the novelty value of an RPi based flight controller, but if you were involved in the design, you must know that's just not true:

RPi A+: 23g, Navio: 24g, Total: 47g

APM Mini: 7g

That's a significant difference in a situation where every gram counts towards flight time.

The Navio also costs 6X an APM mini, and that's before you add the RPi and power module, which brings it to 8X.

I get why someone might develop this as a hobby project, but I can't think why anyone would buy one.