The major difference between the TackForm Steady Clip and the previously reviewed TackForm C-Fit is the way that the two mounting systems hold your phone.
The Steady Clip uses a sort of spring-loaded grip that you open and close by squeezing a pair of levers on the back of the clip. The Steady Clip can hold much larger devices than the C-Fit can, expanding to hold devices up to 4 inches wide. If you're using your Samsung Galaxy Note 2 or are planning to use the upcoming Galaxy Mega to navigate, the Steady Clip is up to the task of holding your handset in place. I tried to cram a Google Nexus 7 in there; it obviously didn't fit.
Because of its design, the Steady Clip can also close its grips completely to hold products that are narrower than the C-Fit's 2.2-inch minimum -- which is great if you're still carrying a Nokia 3310 around.
Because it has levers to open its jaws with, the Steady Clip is easier to get your phone into and out of than the C-Fit (or the mechanically identical Bracketron Mi-T Grip), but it does require two hands to do so.
The trade-off for the Steady Clip's wider range and easier access is that it doesn't seem to hold devices between its rubber grip pads as well as the C-Fit does. I was able to shake my Galaxy Nexus free by holding the mount by its base and shaking vigorously. To be fair, that's more G-force than the average phone will experience when suction-cupped to your car's dashboard or windshield; so as long as you don't run your car into a tree at 45mph or navigate around a racetrack at breakneck speeds, the Steady Clip's grip on your phone is probably strong enough.
Like the rest of the TackForm lineup, the Steady Clip has a suction cup at the base that is made of a tacky, semiadhesive gel that can stick to most solid surfaces in its own right. This stickiness combined with the suction generated by locking the TackForm gel suction cup in place with a lever resulted in a remarkably strong grip on whatever surface I mounted it on. This is a boon for keeping a smartphone secured and stable while driving, but it can also be a tad difficult (though not impossible) to remove between trips.
The tacky material has a tendency to pick up lint and dirt when the mount is stored or transported without a cover, so the Steady Clip is probably best left, semipermanently, in place in your vehicle between trips, rather than being repeatedly placed and removed like a conventional suction cup mount. If the grip does get dirty and lose its stickiness, it can be cleaned with soapy water and a wet cloth. When the cup dries, it will be sticky again.