Honestly though, when you are speaking to a Brasileiro in person, this is how it sounds. Phrases like "o ovo" and "um ovo" naturally are confused because of their similar pronunciatons, especially when a person is speaking at a fairly quick pace. The recordings, for the most part, are pretty on point. The accent of the recording reflects the accents found in southern Brasil.
I'm not certain, but I believe that all of the "recordings" that Duolingo uses are just the Google Translate voices--so, yes, the recording is bad, but it's Google's fault and not Duolingo's. If Duolingo provided their own custom recordings for all of their lessons and languages, they would likely not be able to remain a free service.
Yeah, well... Google, as we all know, just records their words and strings them together in each sentence you type (aka the easy way). Duolingo literally writes their own sentences, so it's not like they need to be prepared for every possible sentence. The way I see it, I think they should have just recorded their own. I never use the voice on Google translate, so I would have no idea if this is Google or not, but sometimes I really doubt that Duolingo recorded the words themselves. And by sometimes... I mean a LOT.
Yes, "eggs are not a vegetable" is such an awkward phrase as it switches from plural to singluar. I think that in the UK (if ever anyone actually said it) it would be more common to hear "eggs are not vegetables".