I find it fine to use. The speaker is a weird idea, but in practice it doesn't bother me at all. The main drawback is having to lift your left finger off the mouse to do a right-click - but you do get used to this fairly quickly. It always gets people who aren't used to it though. Now when I use the mouse on my Windows computer, i lift my finger involuntarily too. Ergonomically it's a bit small but it works (warning: my hands are weird, results may vary). The click/scroll wheel I find great - I prefer it to any others I've tried. The side squeeze button works alright too, as soon as you figure out its not supposed to be two buttons.
Bottom line, it works fine, looks nice. There are definitely a number of more ergonomic mice on the market. I use it on my iMac at home because I have no problems with it, it suits me just fine and because I'm horribly superficial.
I don't have any slow cursor response. You can adjust sensitivity and so on in System Preferences.