Well at least it is means to compare boats on the same level! After applying it to a few I find it pretty useful. I know what to expect from a boat with 100 or 92.
BTW Free ship doesn't give this, I have to calculate it.

Here is the quote from Bear Moutain boats:

Stability Factor
We wanted to give our customers a reference for the stability of our boats. Our designer Steve Killing came up with the stability factor: the technical description is at the bottom of this page, but the real value is in comparing with other boats. Numbers range from about 70 to 120 - the larger the value, the greater the sideways stability. Many novice kayakers find boats below 95 to be just a bit skitterish, around 100 to be average and over 105 to be very stable. Your experience level will determine the stability you need. ....