Do they really help to fetch targeted visitors?
You bet it helps, in less than 24 hrs TweetAdder found me 17,000 Twitter persons to follow in my niche and I'm just beginning.
I added them in various ways. Using a search like you did but also by importing Twitter lists of groups of people or by entering the name of a leader in my field with 1000s of followers so that TweetAdder can download his/her list of followers and add it to the list of people to follow.
Of course they won't all follow me back but the more people you follow, the more you end up as followers and from there it's just a matter of time before contact and sales are made.
Mtlinfo
Just downloaded and logged in but unable to operate
What if a significant quantity of those followers are also other software users trying to gain followers?
Maybe that's the case in the Internet Marketing field but not in my field.
Of course they won't all follow me back but the more people you follow, the more you end up as followers and from there it's just a matter of time before contact and sales are made.