yeah if you think the yahoo mail app is great and fast, then you obviously haven't set up IMAP correctly. Yahoo mail doesn't just not work on my phone, but it doesn't work on many other ppl's phones as well. Just read the reviews on the app and you'll know what a POS it is. Yahoo has very bad Android programmers...
I really don't care what does, or does not work on other people's phones. If it works on mine, it works. If it doesn't, I delete it.
Same thing with reviews. I actually have a brain, and can decide for my self whether an app is useful for my purposes or not.
And since I don't know any of Yahoo's android programmers, I won't be so bold as to suggest that they are "very bad."