Q: I receive a message saying "hdmi out is, not supported by this application" I can hear the sound but receive no picture when trying to watch Sky Go.

That's correct. The developers have blocked this

it would if sky go would the sales person would be unlikely to know which apps block these features

but of cause thats not reason not to return it

of cause sky could change their policies down the line

though since it say hdmi out rather then airplay then I would likley because it also block

using the hdmi out converter for ios devices just in case you were wondering if you should get one of those in place of the appeltv