To answer your question I would need to know what screener settings you are using. When I'm loading default "Rule #1" settings, it shows filters by Growth Grades, Debt/FCF ratio and trade volume. As you can see, there is no filter by value price!
Essentially, we are looking for stable companies, with low debt and good stable growth. Therefore in the result set I got, there are few companies with negative MOS and a few with positive.
Usually, there are not so many companies that meet all the criteria and it is very easy to filter out those that look overpriced. On top of that, you may want to give some companies a slack because of their wonderful business, great CEO or whatever other reason it might be. To give user that flexibility, we had to get rid of the filter by value price.
I hope this helps.