When I picked up the PanaVise 15508 Portagrip, something about this smartphone mount seemed familiar. Looking at the suction cup base and the adjustable gimbal for the phone clamp, I realized that part of this unit is the same thing we at CNET use to mount cameras to the outsides of cars.
I've attached a similar clamp, holding a GoPro, to a car's fender, and driven really, really fast.
That should serve as testament to how well the suction cup holds and the durability of the arm and gimbal. But the 15508 Portagrip has a smartphone clamp instead of a camera mount, and is intended for the lighter duty of attaching to a windshield, and remaining inside the car.
The suction cup end uses a metal cap. In its center sits a big plastic button, helpfully labeled "Press." Do as the button says, then pull up the lever straddling the button, the suction cup grips any smooth surface like a barnacle.
A bracket sticks up from the suction cup and holds a short, 4-inch arm at a single hinge point. That hinge lets the arm move through about a 150 degree arc and has a screw in the bracket to lock it down.
What gives the 15508 Portagrip some of the best adjustability I've seen among smartphone mounts is the gimbal at the clamp end of the mounting arm. Loosen the bolt in its metal cap, and the gimbal lets the clamp twist and turn with remarkable versatility. Once you get the right position, tighten the locking bolt, and the mount becomes immobile.
The suction cup, arm, and gimbal portion of the 15508 Portagrip is the best I've seen for a windshield mount.
The phone clamp is the same piece that PanaVise uses on the 15504 Portagrip, the little brother to the 15508 model. This clamp has a soft backing, so as not to mar any smartphone placed in its care. The short, or bottom end of the clamp, has two little feet that swivel so they can be pushed out of the way.
Two spring-loaded ratcheting arms do the job of holding a smartphone in place.
At the press of a button, the arms pop out, opening up to a 3.75-inch width. That means it will easily hold a Samsung Galaxy S4, and even smaller tablets. After placing a smartphone between the clamp arms of the 15508 PortaGrip, push them together and they ratchet closed, holding the smartphone firmly in place.
With the 15508 PortaGrip suction-cupped to a windshield, I found I could operate the clamp with one hand, simultaneously holding my phone against its soft backing and squeezing the clamp arms together. Pushing the button to pop open the arms, I quickly learned to keep a grip on the phone, lest it fall out and hide under the car's seat.
I used the 15508 Portagrip on a road trip, suction-cupped to the windshield while I drove over a variety of mountain roads in temperatures occasionally hitting 100 degrees. The mount proved immovable, never once losing its grip on the windshield or slipping from the way I had adjusted it. The clamp was always in the position I had set it, ready for my phone.
Given the design of the clamp arms, this mount is intended to hold a phone in a vertical position. The gimbal allows it to be swiveled to horizontal, and tabs on the clamp arm can be moved to grip the phone closer to its center, but the narrowness of those tabs made for a questionable horizontal hold.
The 15508 Portagrip lacks any USB pass-throughs or cable runs, so you will have to deal with any cable clean-up yourself.
Virtue in strength
PanaVise makes a good selection of heavy-duty mounts, but the 15508 Portagrip is kind of the king-daddy of the set. In fact, it is the strongest and most durable mount I have seen anywhere. A combination of metal and strong plastic components give it a substantial feel. And though it only has two adjustment screws for the arm, they give it an excellent range of motion. For cars where the windshield is far from the driver, the four inch arm may not be long enough to put the phone clamp within range of the driver, but Panavise sells an extension piece, so the mount can be modified.
The lack of a good horizontal positioning for the phone clamp is a drawback, but otherwise the ratcheting arms work well holding a phone in place. Although the clamp looked clumsy at first, I found it reasonable to operate with one hand.