I've had a set of Keo Carbon Tis since they first came out, think it's about 5 years now, also got Classics on the winter bike. I changed from SPD-SLs, the Keos are great in use, slightly smaller making clipping in slightly harder IMO, but not difficult.
The cleats do only last about 10 minutes though, and they've recently made them far worse by putting 'non slip' stuff on. Now they 'stick' to the pedal for the first 6 minutes making clipping in harder, then the rubber starts coming off and the plastic wears even quicker!
Both my pairs also 'tick' when you're out of the saddle. I'm very tempted back to SPD-SLs, although less so now they're so expensive!
I must say that I do find road pedals more stable than MTB ones, even with stiff soles, there must be a bit of 'rock' in the pedal body or between cleat and pedal which is reduced with the larger contact patch. When I have used MTB pedals and stiff MTB shoes on the road it doesn't feel anywhere near as nice.