These SFS, as they are called 'DROPS', have their cons and pros.
Pros: you can get exposed to multiple pages of different models, and the more drops you do, the better.
Yes you can get lots of subscribers/followers daily, but thats usually for free pages because paid drops are done by already active pages, because nobody wants to share their active & paying fans with someone who doesnt have them at all.
However, cons:
people filter and hide your's page feed so they are not getting notified to your posts from the wall and this could harm your likes/activity status, which will potentially kill your page.
people block your page as you keep spamming over and over again to gain more.
So this is a give=lose mechanism.
The best is to buy promotions, way better than doing drops.
But I heard from different models that earned around 3-5k$ just by doing DROPS/SFS.