I think that if one wants to do a special, promoting it through Angie's list isn't a bad idea. Generally, consumers are wary, I think, of "special" prices from companies they don't know. And most people don't know anyone. They are also inclined to be more suspiciious and demanding of companies that offer specials in general. There is no question that Angie adds legitimacy behind the special.
However, in general, I think that it's not worth advertising with them. I have a guy that I found on Angie's list called the Neighborhood Telephone Man. Teeny category so he didn't need to stand out. What he does is that he comes to your home (or business) and fixes your phones for a reasonable charge. Just like your local phone company used to do until things changed and you needed either to pay extra for inside wire maintenance or extortionate prices if you didn't have it and something went wrong in your house. Cable systems provide affordable phone service but just hook it up to your existing inside wiring and (at least here) don't do inside wire maintenance. This guy retired from Verizon and started doing this on a small scale and just got more and more work. He's the kind of guy who would be welcome anywhere. Tall, pleasant-looking, extremely low-key and unexciteable, polite and very knowledgeable. And he'll do anything from put in a jack to put in a business key system, or crawl through your attic to find a broken wire. And he is very reasonably-priced. It's like having a next door neighbor who works for the phone company, has all the right tools in his garage, and is happy to come over and help you on the rare occasion when you have a phone problem. So naturally I gave him a stellar and detailed review on Angie's list. As did about ten other people. So he got that Circle of Happiness award, and Angie's List started bombarding him asking him to advertise. I did the math with him on how much more business he would have to get just to cover the ads, and it wasn't pretty. Better to just put that logo and award on a few thousand business cards from VistaPrint, and leave them in car washes, restaurants, the deli, etc., in every community into which he is called, along with a concise description of his service (which a lot of people need once in their lives). And leave a brightly-colored sticker near the phone box and wherever the homeowner keeps his/her stickers for the plumber, electrician, etc. That has, I think, worked out very well for him, and for a lot less money. Meanwhile, I think the real benefit of Angie's list is to check out someone who was recommended to you, or whose ad looked appealing, or whose truck you have seen in the neighborhood. I have done that for anyone who we have thought of hiring. I would say that 20% of the time I look for a new contractor on Angie's List, and 80% of the time I am checking out a source that otherwise came to my attention. No question that Angie provides legitimacy and much more reliable reviews than, say, Yelp. But I personally think it's a better deal for the contractor to leverage that legitimacy through other more direct advertising media. (It IS helpful in finding an off the beaten path trade. In my case, we found the telephone guy and a really-service-oriented, fastidious, asbestos removal guy through them. Both small categories.)