I see lots of people recommending K9, but despite trying it several times, I can't figure out why. It does support some additional features, but lacks features

I see lots of people recommending K9, but despite trying it several times, I can't figure out why. It does support some additional features, but lacks features the stock Android mail app has (like push Exchange). It's also just as ugly and unresponsive as the stock mail app. Other than the gmail app (which I think is pretty decent), decent mail apps are still a wide open opportunity (IMHO) for Android developers.