I've used them for the past 5 years and will NOT be going back to other cleats. I have Titanium Zeros I got for a bargain and have never looked back. As far as clipping in and out goes....like everything its a feel thing......Clipping in becomes second nature.....
Yeh strange at first - as is the 15 degrees (approx) of float (adjustable heel in or heel out) it sometimes feels like your ice skating.
Once you adjust the amount of float which is right for you the cleats and pedals work beautifully. I have mine set to 6 degrees heel in and out. Never had knee problems since I have been using them.

I remember when I first used them I'd get on the bike inside under a doorway, support myself and practice clipping in and out.
You cant go wrong.
Anyways Speedplays Zeros are amazing. If they werent the pro's wouldnt use em!!!!!