Thanks for that - guess we'll have to wait for this to get in folks hands to actually know. But doesn't look likely my hoped for solution will work.
So here is what Yuneec USA had to say about using an E90 and a H520 controller with the H Plus:
Thank you for contacting Yuneec! Unfortunately, that is not possible due to the fact that the E90 uses different software than the camera that is available on H Plus, so the drone will not recognize it as a compatible device. Also, the controller software you have on your ST16S is different than that on the H Plus ST16S, so they would not be able to work together properly either. Hope this information helps and if you have any other questions, please feel free to contact us.
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So I will soon have my H520 for sale - whats the best way to advertise that do you folks think? And what would put as a price - H520, original 2 batts, one charger, two sets of props (or are the props at least the same?)