It's a pretty foolproof system for making just about any device easy to access and see. ProClip USA's website lets you find a mounting plate that will work with your specific make and model car and then select the appropriate adapter plate to attach the device you want to use. In my case, I got the ProClip Left Mount for my WRX STI along with the 2 Prong (Dual-T) Mounting Plate with Tilt Swivel to use with my COBB V3 Holster. The ProClip mount comes with double-sided tape on the back side of each arm, but I didn't use it at first so that I could test-fit things and see what angle I wanted the mount to be at. There were also four self-tapping screws included with the adapter plate that screw tightly into the mounting plate. I found that attaching the adapter plate to the mounting plate was best when it wasn't attached to the car, so I was glad I hadn't used that double-sided tape to permanently install it just yet!
Things really fit like a glove when I installed everything. The colors and textures on my STI's A-pillar matched up with the mounting plate great and the adapter plate connected with the COBB V3 Holster nice and tight. There were no noticeable rattling or loose fitting parts, but it also was not so tight that you couldn't move things. The swivel base on the adapter plate was easy to adjust and the 2 Prong mounts still let me detatch the COBB V3 Holster with minimal effort. This was important to me, as I didn't want to struggle with making adjustments but I also wanted it to be secure. The roads in my area are bumpy, uneven, and ridden with potholes so I was really pleased to see how well the ProClip stuff worked.
In the month that I've had the clip installed, I have yet to experience any issues with it. October and November are transitional periods for weather here in the Midwest, and sometimes the back-and-forth mix of warm and cold days can cause creaks and rattles with the plastics used in Subaru interiors. The ProClip Left Mount, Dual-T adapter plate, and the COBB V3 holster were steadfast all month long and continue to be. In fact, the COBB Access Port accessories page even lists ProClip products like this one on their own website for the performance cars they tune with there. Just recently I remembered that I still hadn't used the double-sided tape on the Pillar Mount, so I was even more surprised that it hadn't shifted or rattled at all for a month! I went ahead and used the tape upon discovering this and, unsurprisingly, have still had no issues.