Hi there, I don't have a lot to add to this, just stumbled upon it looking for a feijoa wine recipe (the trees are going mental here at the moment, and people had absolutely tons to give away). Anyway, they are actually quit different to golden kiwifruit. Here's a link to Wikipedia with some info..... http://en.wikipedia.org/wiki/Feijoa
it's not uncommon to be used to make sparkling wine here, but I've never heard of it being used in mead, that's not to say it isn't possible. Good luck!