are oyu sure about this, that Fb is OK with affiliate link?
Well I can only speak from my own experience. But I already promoted several affiliate links (from both clickbank and shareIt), and they never got disapproved (at least not because of the ad destination, just some issues with the images/ad content sometimes).
I have to say though, that the campaigns never really were successful.
With Facebook you have to do a "softer" approach, since people are not on Facebook to buy anything.
I think you can get both a better CTR and more sales if you promote your niche-related page first, and then use social proof tactics to promote your affiliate links.
For example what I think could work very well is to make a post where you put your affiliate link, then ask something like "So does anyone of you guys use [your product]? Looks quite good to me.", and THEN use a few fake accounts to post comments like "yeah I have this, gotta say it's pretty awesome".
This should both prevent any further bad comments about the product and on the other hand make people feel like they are missing out on something.
Social engineering at it's best.