The K100 attaches easily to a car visor with the sturdy but bulky preaffixed metal clip. The unit did not budge during my jaunts in the car, and removing it from the visor required just a quick tug.

Once I got the lay of the land--the only controls you need all sit in a row--I found the K100 a cinch to use when driving. For starters, all the buttons are large. With my eyes on the road, I could easily locate the power/call button, which sits in the very middle of the row. So when I wanted to dial by voice ("Call Tim office," say), I simply held down this main button with my thumb for about 2 seconds to initiate my phone's voice-command feature. Or I could do a quick double-tap to redial the last outgoing number. The main button is surrounded by a ridged volume wheel, and the mute button and FM-transmitter control are on either side of the main button.

The buttons delivered an excellent response when I pressed them; I liked not having to press them very hard to get such well-defined tactile feedback. Even though the clickety-clack sounds are loud, it didn't bother my passengers or me.

On the volume wheel, in contrast, I needed to do quite a bit of thumbing to make the adjustments I wanted.

Voices coming through the K100 sounded clear. At the other end, according to my callers, I sounded a tad muffled overall, but folks could hear what I was talking about; generally my words did not break up, nor did listeners complain about static. Only a handful of words here and there sounded stuttered. In fact, one caller commented that--unlike other models in this particular product category--the K100 didn't sound too speakerphone-like.