Is Facebook advertising for a reader magnet worth it?

I’ve been running small Facebook ads for growing my list using my reader magnet for a few months now. I’ve supplemented with some AuthorXP list purchases.

If I look at the last few months of Facebook: CTR: 5%, CPC $.14, link clicks 858 (but I have no way of tracking who fills out the web form since I don’t manually collect that form) with a $5 daily budget.

I’m not sure how to quantify what AuthorXP provides given that some people attrit/unsub from the file.

It’s hard to know if I need to keep spending around $200/mo on Facebook or if now that my list is around 1,500 that maybe I should take the Facebook $$ and put that towards Amazon ads since I will launch my book this November. Any suggestions?