Since this is a rule for whether you should open the bidding, the result of opening these hands should be better then the average pass out deals and also better then the other side. There is no preemptive value in a regular opening at the one level. The average number of tricks for hands just pass the rule of 15 is 8.87 vs. 8.2 for the conservative pass out deals and 7.8 for the opponent side. If you open all hands using rule of 20 your side will have a significantly advantage. But the rule of 20 includes a lot of hands which you will open anyway without using the rule of 20. So let us examine the situation a little bit more closely.
Let us first look at the conservative pass out deals of 12 or less high card length points. We will add the rule of 20 to the north hand and see what happens. The average number of tricks for hands just pass the rule of 15 is 8.71 vs. 8.2 for the conservative pass out deals and 7.83 for the opponent side. If you have a hand which has 12 or less high card length points and it passes the rule of 20 you should open the hand. It is a great advantage for your side.
Let us look at the most restrictive pass out deals with 11 or less high card length points. The computer program say there is no hand that can pass the rule of 20 and has 11 or less high card length points.
It turns out that rule of 20 include all 13 or more high card point hands; all 12 high card point hands except 4333 distribution; all 11 high card point hands except hands with no 5 card suit or 5332.
Let us look at two cases with 11 high card points and top two long suits of 8. The average number of tricks for hands with11 high card point and 5332 distribution is 8.27 with the other side taking 7.95 tricks. The average number of tricks for hands with11 high card point and 4441 distribution is 8.75 with the other side taking 7.8 tricks. The rule of 20 fails to select these 2 profitable situations. There is no surprise regarding this result. You can see the value of different hand patterns in the previous section and 4441 is very powerful; better then 6322 and 5422.