These are actually quite handy. What you want to know:
You need TWO wrenches to tighten it. One should be a (thin) fixed open-end wrench (IIRC, 9/16"), to hold the nut under the knob in a fixed position while tightening the nut on the end of the bolt. If you try to use a (thicker) adjustable wrench on the inside nut, you run the risk of cracking the knob.
They are often called a “suicide knob”, don’t let that scare you. The human default is to install the knob to the outside of the wheel, more torque or leverage that way, but that would be wrong and unnecessary. The correct way to install it is with the knob and its bolt INSIDE the steering wheel, the smaller hinge on the outside of the wheel. In this position, you get plenty of leverage, especially with ubiquitous power steering, and it does not hit your legs, or more sensitive organs. Remember the “good” old days, of manual steering unwinding several spins very quickly, as the car straightened from a tight turn. 
It has a piece of plastic/rubber inside the clamping bracket. Adjust its length and thickness, so that the clamping bracket, when bolted solidly, places a bit of tension on the clamp. I had to cut 1/2" off the plastic band, and I added a hidden piece of electrical tape onto the plastic strip, to add thickness at bottom, top and hinge.
The first time I installed it, I adjusted the nut at the bottom of the knob a bit too loose. I realized that during a short test drive. It did not leave enough depth of the bolt as an axle in the knob, and the knob would have broken in short order.
I bought a set of 3 units (spares), as I have had spinners since 1975, and they sometimes break, though I have not had a break with this model. Install it right & it will last long. My last one, on a now retired auto, was going strong after 6 years.
The one I grabbed from my three-pack, had a small bit of mis-formed metal, on the flattened end of the hinge rivet, which I used a file to smooth and a bit of black paint to hide the shine. I also used a stretchable wheel cover, to hide the bracket and soften my wheel. (new ‘25 Subaru Outback).
Do your OWN research, especially visit your State’s DMV or state laws’ website. If you tend to get stopped a lot, print and carry your evidence, to avoid ill-informed but-hungry sharks. But, YES, these DO appear to be legal in all 50. I am in Virginia, a fairly ANAL state law-wise. Radar detectors are illegal in VA, and we have annual certified-mechanic Safety Inspections (a worthwhile annual PITA). One car was rejected for a piece of window tinting, blocking sunlight around the rearview mirror. I have gone 6 years of inspections without a hiccup from having a steering knob.
The last one, I placed at the “2” o’clock position, I put this one at “10”; gives me something for my weaker left hand to hang on to, freeing my right for other controls. Be sure to look for where/how airbags works and don’t block.
These also come in black (on Amazon) and there are other more expensive varieties, that I rejected for various reasons before my purchasing black for my last car.
Drive happy!
I want to find one in black. My steering wheel is debatably too large for this to fit (I’ll need some dimensions, please). I have one spinner which is due to wear out (after 5-6 years), so this is timely.