Here's a photo of the first one I had for a couple of years. It sits pretty nicely on a non-slip pad in the corner near the driver-side A-pillar. It has never slipped off the pad. I've got my new one in the same spot.
The first one that I bought I had to recharge with a USB cable about once every couple of months since the car is in the garage most of the time and the solar panel doesn't have time to keep it charged. The second one that I bought seems to have a better internal battery. I don't recall charging it yet and I've had it for six months or so. Both of the units that I've had paired up automatically with each sensor and never lost their connections. And I've never had one of the sensor-caps leak air. Each one has an O-ring to help seal it. When you unscrew a sensor-cap to add air, the control unit will start beeping...but it reconnects automatically after you screw the sensor back onto the valve.

It's interesting to see how the tires heat up on a hot Texas day! You can watch the tire temperatures and pressure go up!