I realize this is an old thread, but I am new to the forum and ran across it and figured I'd give my HA experience.
Personally, for us, it works great. I set a monthly budget (ex. $500.00) Each lead is 14.00-25.00 In my line of work, it's pretty standard that no one is giving "free estimates". All of my competitors along with myself have a standard truck trip that is charged before going to the house. (if not they don't stay in business long) Once inspection and estimate of repairs are given if the customer chooses to have us do the work we knock of the inspection fee. If they choose to think on it for a bit, then I've made a small amount of money and covered my expenses. There are times where HA absolutely stinks, the calls that come in are tire kickers, wont call you back or respond to emails, etc. It's all part of the game I guess.
During my busy season when I'm dealing with repeat clients I adjust my monthly budget a little lower which in turn keeps my phone from ringing while I'm working.
You can throw all the money you want in your monthly budget, if the leads arent there you arent getting charged. Period. There are months where I do not exhaust my monthly budget.
Over the years, I've done almost every type of advertising you can think of. For me, HA has been a huge ROI. Also, once I make contact with that customer, they no longer go through HA for my services ever again. Business cards, follow up emails, etc. Forward scheduling all ensure that I never pay for that customer again. Not to mention the referrals I get from these jobs. Also, once I have that customers lead information (after all, I paid for it) I keep their info. Even the leads that I did not make contact with or the ones that I didn't win the job. They are all on my annual mailing list in which my postcards I sent out just before my season approaches. I can't begin to tell you how many people call and say, I'm glad you sent this to me the company I chose last year is out of business or they weren't happy with them.
I can see where for some businesses HA simply would not work. It is and can be a headache at times.