More effective than any ad, and lower in cost than any other sales campaign, bar none. A whole campaign can be waged without ever having to pick up the phone. The most effective campaign I have ever written was a series of personal letters. A campaign is not a single effort of anything. Write a short series of letters and send them to your best prospects over a selected time frame in a program that takes your best prospects more seriously than just sending one letter.
Direct mail is a game of numbers.
Well, now mail 100, get 4 more sales. Now mail 1,000 - get 40 sales. By the way, to test a new list, the industry standard is to mail 5,000 pieces. As broad as your vision may be, you can only see your business from your own singular perspective. Ask open-ended questions, then listen.