Using FFA Pages to help build your list is a reasonable approach provided you have your expectations set realistically.
Realize that FFA Pages are used by people that are advertising whatever it is that they have for sale. They want to sell their stuff. That's why they are adding links to FFA Pages.
They add or post their links to FFA Pages with the intent of getting their own web site promoted. They recognize that the trade-off is that they agree to receive ads from the owners of the various FFAS Pages to which their links are added.
What this means is that your ad will go out to these folks but it will go out along with several (sometimes hundreds or even thousands of) other ads.
To be effective, the ad you send out to people posting their links to your FFA Page has to have a compelling subject line. It needs to state clearly what the primary benefit is to the reader so that if they are interested, they will be compelled to open the email and read more about your offer.
Some of the worst subject lines include things like:
"Thanks for adding your link".
"Your link has been posted".
"I got your ad".
These subject lines are essentially worthless as they just scream out, "Hey, Buddy! Here's an ad I'm sending because of the ad you posted on my FFA Page!". Believe me... nothing will cause that reader to reach for their DELETE key faster!
Instead, focus your subject line on the most important benefit of your offer. And make it SIZZLE (without too much hype). There's a fine balance between being exciting and crossing over to the land of hype. Testing and patience are the key to this little trick.
I use my own FFA Page to generate leads. It's nowhere near my most successful tool for generating solid leads but it generates anywhere from 1 to 3 new requests per day. From there, my AutoResponder takes over and follows up with those leads.
I think of my FFA Page as an "add-on". I certainly don't focus much on it. I set up my ad. I track the ad to be sure it's getting some results (that's how I know I get 1 to 3 new requests from it per day) and then I just let it run.
It does its thing in the background and I focus on other advertising such as articles, search engine optimization, other classified ads, etc... all geared toward getting prospects to request my information. Once they do, I have their information in my AutoResponder and that wonderful little tool begins the process of following up and building rapport.